During Harry's first mission on Voyager the ship is presumed lost in the Badlands while chasing a Maquis vessel. Sitting at the Operations station, Harry finds himself thrust into the most demanding position that he could have ever imagined as the Voyager is transported 70,000 light years from home into the Delta Quadrant. Truly away from home for the first time, Harry struggles with the sense of loss. He had anticipated being away from Earth for long periods of time, but had not expected to be so completely separated from his family. Harry especially misses his girlfriend Libby, and it takes time for him to consider forming a relationship with anyone else. Perhaps more deeply affected than most other crew members, he puts his energy into his work. In the years that follow, Harry learns to adjust and finds comfort in the new friends around him. Janeway seems to understand Harry sometimes you see the affection she has for this very young man and she is aware of how he in particular misses his home and family, he is the youngest member of the crew, and now she is responsible for his well being.

Harry enjoys several holodeck recreation programs, including playing the title role in a holodeck novel version of the epic poem Beowulf. He also finds time to work on a new orchestral program with Lt. Susan IMicoletti, who plays the oboe. Kim’s friendship with Tom Paris also widens his personal interests, particularly in holodeck tastes. spend a great deal of time together in a recreation of Chez Sandrine's, set in Marseilles, France. Tom Paris often visited this waterfront establishment while he was at Starfleet Academy. The bar has a pool table, numerous beverages, a selection of lovely ladies, and sleazy locals the perfect holodeck venue for the two young officers looking for somewhere to relax. The two men have become very good friends .

Harry is a talented clarinet player and was a member of a youth orchestra. Stranded in the Delta Quadrant, he has replicated an instrument and practices regularly. In his thoughts can hear his mother saying practice Harry practice .Kim often relaxes in his quarters by playing classical music on his clarinet. He acquired the instrument on Voyager by saving up his replicator rations for an entire week.

It is his job to monitor the condition of the ship and to assess any damage. He has also taken shifts in Engineering. the ship. Responsible and reliable though Harry is, he can also be a stubborn and defiant engineer, the kind who, once he makes up his mind to do something, cannot be kept from going ahead with it. He proved himself to be an excellent Starfleet officer and has more than fulfilled the early promise he showed at Starfleet These roles require someone who stands firm under pressure and acts with a clear mind. Harry is very much an optimist and a forward thinker. despite his relative inexperience. Harry is an excellent bridge officer. He has a particular aptitude for science and has often proved himself to be an invaluable member of the crew.

Harry's knowledge of wormhole gravitational eddies and spatial dimensions proves beneficial when a probe from the Voyager gets stuck. Using the probe as a relay, he is able to send a transmission to the Alpha Quadrant. Although Harry's initial exuberance is quieted by the fact that their messages will probably never reach home, he is calm a deep thinker his determination and quick thinking proves his value to the rest of the bridge officers. Harry’s engineering skills are particularly valuable to the crew, who cannot make regular layer overs for maintenance and repairs.

Early in his existence, the E.M.H lacks the social niceties that other beings take for granted, exhibiting , a brusque and off hand manner with the Voyager, crew he treats. His terse nature is appoint of contention between the Doctor and members of the crew such as Tom Paris and B'Elanna Torres, but it is the friendship of the young Ocampa  girl  Kes that initially leads him to consider changing his attitude. Kes becomes his nurse and she is taught by the doctor. Because his bedside manner remains somewhat dry and acerbic. When the Doctor is accused of having no empathy with his patients, he decides to find out what it is like to be ill. Kes  reprogrammed the time he sets, so he suffers longer thus enabling him to better understand the suffering of the crew, soon after this his bad behaviour of his early days drops away as he begins to connect with his crewmates and patients. The first clear signs that the Doctor is on the road to humanity.

One of the first modifications comes when Captain Janeway gives the E.M.H control of his own deactivation . As a sentient being of sorts, he finds it annoying that members of the crew treat him like a computer program. Now the Doctor has the ability to turn himself off and on this allows him a new level of independence. In turn, this helps others to see the Doctor as a person rather than just a program. One negative side effect of being designed only for short term use is that any extended period of operation increases the chance that the E.M.H program will become corrupted.

Normally, a Starfleet technical maintenance layover at a Starbase would soon sort this out, however due to Voyager's remote location, such maintenance is not possible. Problems do arise two years of intensive use and many subroutine modifications, the Doctor begins to show signs of marked memory degradation. It is discovered that the EMH program is suffering a cascade failure, a disorder which is causing a memory loss. This is first thought to be treatable only by a complete re-initialisation of the E.M.H program, a procedure that would effectively delete all the Doctor's experiences and personal growth since he was brought online. Lt. B'Elanna Torres runs a Dr. Lewis Zimmerman diagnostic holographic program and upon whom Voyager's Doctor is patterned both physically and intellectually. By employing a and risky procedure, the diagnostic program's matrix is layered onto the Doctor's failing program, creating circuitry changes which restores the E.M.H to full working order. he did lose some of his memories but soon re learns.

The Doctor’s greatest steps toward humanity, come not from his development but the emotional growth of the rescued the former Borg drone Seven of Nine. At First Seven's attitude toward the crew resembles the Doctor's in his early days, and the Doctor sees in her what Kes saw in him three years earlier. The Doctor takes it upon himself to become Seven's mentor in social and emotional situations, and despite the fact he is not human, both he and Seven begin to learn from one another as he helps her he is in fact helping himself. The Doctor's years of activation give him much more experience than Medical Hologram's programming are meant to have. The Doctor even finds himself falling in love with Seven, and though his feelings are not reciprocated, he is pleased to learn that she values his company very highly.

2373, an accident sends the U.S.S. Voyager to Earth, 1996. Here, the Doctor’s program is downloaded from the orbiting Voyager, by the computer genius Henry Starling, who then provides the Doctor with a holo-emitter created with stolen  29th-century Federation technology. The holo-emitter is a small device, worn on the sleeve, that can transmit holographic programmes without any additional equipment. The entire E.M.H program can be downloaded into it; The Doctor can now go anywhere, on or off the ship. As long as the Doctor wears the device and nothing damages it, he is free.

If personnel. are injured The Doctor is now able to beam down to a planet's surface to help out. the Doctor eagerly volunteers for an away mission to a Garan mine; the prospectors have become infected with an unknown virus. He is perfect for the job, not only because he is a doctor, but because he cannot be infected. The Doctor visits the mines and is amazed by everything he encounters. At first, Chakotay feels that he is easily distracted and suggests he concentrate on more significant matters, but by the end of the mission Chakotay assesses the Doctor's performance as perfect.

He is also able to fall in love. When a very ill Vidiian woman is beamed aboard, the Doctor creates a healthy holographic program for her mind to reside in while he tries to heal her body. She appreciates his intelligence and humour, and he appreciates her sweetness and honesty. When she decides that she would rather let her body die than risk losing his love because of her illness, he convinces her that it is her soul that he's fallen in love with. They spend two weeks together, dancing on the holodeck in a new dance program he creates , he is guided a little by Tom Paris for these emotions are new to the Doctor. 

The EMH's most important and dramatic away mission comes a few months later. Seven of Nine's new and improved astrometrics lab leads to the discovery of a vast network of alien communication stations, the most distant of which is within sensor range of the U.S.S. Prometheus, a Federation ship in the alpha Quadrant. The Captain proposes sending the Doctor 60,000 light years through the communication network, there is grave danger that his program may be lost, he accepts the mission. created for the Prometheus - and learns that the ship has been taken over by Romulans who have killed he is able to completes his mission orders, the delivery of a message regarding Voyager's survival to the Federation authorities.

The Doctor is involved with Seven 's unique situation from the moment Captain Kathryn Janeway makes the decision to help the former Borg drone rejoin humanity. The Doctor continues to treat Seven throughout the painful physical transformation that follows; Seven has to report for check ups as her human systems reassert themselves following years of suppression by her Borg transplants After a few weeks, the Doctor pronounces system fully functional , but the hologram soon recognizes that this is not the end of her transformation . When Seven attends a celebration in the mess hall, she clearly finds the social situation uncomfortable, and the Doctor takes it upon himself to instruct her in the social graces. Given his own education in this area aboard Voyager, he considers himself to be the obvious person to play mentor to Seven. They engage in small talk exercises using the holodeck, in which the Doctor points out that successful conversation involves letting the other party answer, listening to what they say.

The Doctor dubs Seven his prize pupil, and proudly watches her progress. They are kindred spirits in many ways, the hologram says that he understands the burden Seven carries of being forced to deal with those who fall short of her excellence. He also simply enjoys her company, and seeks her out when in need of a logical mind. The Doctor talks to Seven about her parents, encourages her to view their personal logs as a way of exploring her childhood. He comforts her when she suffers disturbing hallucinations about the Borg , and later when she is afflicted by multiple personalities from her time in the collective. 

'The Doctor's relationship with seven gets off to a difficult start: Captain Janeway orders him to remove 'Seven's implants against the Borg's wishes. the Doctor slowly realizes he has fallen in love with Seven of Nine, but knows that his feelings are not reciprocated by the ex-drone. Seven admires the Doctor's clear thinking and lack of extraneous emotion. She vigorously argues on his behalf when Janeway intends to rewrite his program, denying him access to a traumatic memory that is creating psychological torment. Seven believes his individuality will be compromised by this course of action he has evolved past his original programming and should be allowed to confront and reconcile the difficult memories. Janeway agree’s with Seven and sits herself for many hours with the Doctor just letting him talk.

Mentor and protégé prove a good team time and again when the pressure is on. During the Hirogen takeover of the ship, the Doctor is able to use Seven's Borg implants to emit a jamming signal, allowing her to deactivate the neural interfaces implanted in the crew. It is the first step toward retaking the ship. Seven immediately turns to the Doctor when the crew are tricked into believing they have found a wormhole home. They work together to free Voyager and another ship from the organism that has snared them. Their friendship goes from strength to strength, in fact this in part is a reflection of the Doctor's success in his own role as mentor, tutor. and friend