As a child in grade school, Harriman read about the legendary missions of the crew of the original Federation starship Enterprise, a fact which he related to James T. Kirk, Montgomery Scott, and Pavel Chekov during the Enterprise-B's christening ceremony in 2293, where the three were guests of honor.
During the Enterprise-B's shakedown cruise, the crew received a distress call from the transport vessel Lakul, which was carrying El-Aurian refugees to Earth. Initially, Harriman was slow to respond and reluctant to attempt a rescue, aware that the Enterprise did not yet have a full crew complement and that several key systems were not installed; however, he was forced to respond as they were the only ship in range. The crew discovered the Lakul and another vessel trapped in a severe gravimetric distortion which was threatening to destroy the ships.
As the crew of the Enterprise could not move into transporter range without becoming trapped in the distortion itself, Harriman suggested a number of courses of action. These suggestions included generating a subspace field around the ships and venting drive plasma from the warp nacelles in an attempt to break them free. Use of a tractor beam was impossible because the system had not yet been installed.
These efforts met with failure, and given it was obvious Kirk was barely restraining himself from intervening, Harriman swallowed his pride during this crisis to ask for the veteran's advice. At that consent, Kirk suggested moving the ship into transporter range that they were able to rescue the surviving passengers. Harriman was initially skeptical of this plan, observing that the gravimetric distortions had the potential to destroy the ship, a claim to which Kirk simply responded, "risk is part of the game, if you want to sit in that chair."
Although the effort was successful and the El-Aurians were beamed aboard, the Enterprise did indeed become caught in a gravimetric field. With no photon torpedoes aboard to generate an antimatter discharge, Scott suggested that a resonance burst from the main deflector might simulate the effect and disrupt the field's hold on the ship long enough to break away. As performing this procedure required a modification to the ship's deflector relays, Harriman granted command to Kirk as he prepared to leave the bridge and perform the modifications. After only seconds in the captain's chair, Kirk maintained that Harriman's place was on the bridge of his ship, so he volunteered to perform the modifications himself. It was during his efforts to modify the relays that an immense energy surge struck the ship, causing a hull breach on Deck 15, where Kirk was working. After the ship broke free of the field due to Kirk's actions, Harriman, Scott, and Chekov traveled to Deck 15 where they discovered that the room in which Kirk was working had been completely destroyed, seemingly resulting in Kirk's death. (Star Trek Generations)
"I just want you to know how excited we all are to have a group of living legends with us on our maiden voyage. ...I remember reading about your missions when I was in grade school."
- - John Harriman, to James T. Kirk, Montgomery Scott and Pavel Chekov (Star Trek Generations)
"How big is your medical staff?"
"The medical staff... doesn't arrive till Tuesday."
- - Pavel Chekov and John Harriman (Star Trek Generations)
"Captain Kirk, I'd be honored if you'd give the order to get underway."
"Thank you very much. I..."
"Please, I insist."
- - John Harriman and James T. Kirk (Star Trek Generations)
"Captain Kirk, ...I would appreciate any suggestions you might have."
"First ...move us within transporter range and beam those people aboard the Enterprise."
"What about the gravimetric distortions? They'll tear us apart."
"Risk is part of the game if you want to sit in that chair."
- - John Harriman and James T. Kirk (Star Trek Generations)
"You did it, Kirk!"
|Commanding officers of the starships Enterprise|
|Enterprise NX-01:||Archer • T'Pol • Tucker • Lorian|
|USS Enterprise:||April • Pike • Kirk • Decker • Spock|
|USS Enterprise-D:||Picard • Riker • Jellico • Halloway|
|ISS Enterprise NX-01:||Forrest|
|ISS Enterprise NCC-1701:||Pike • Kirk • Spock|
|USS Enterprise:||Pike • Kirk|
Harriman was played by actor Alan Ruck.
The script for Star Trek Generations describes Harriman as, "young, confident, eager – this is his first command and he takes it very seriously." 
Alan Ruck describes his casting as Harriman thusly:
This is crazy. So my manager at the time calls up – and this is in the days of faxes – and says, "I'm faxing you over some pages for a Star Trek movie." I say, "Okay, great." And the pages come over, and I read them, and in my mind I'm going to be playing an alien with a head shaped like a stalk of broccoli or something. So I go, "Who do they want me to play?" "Harriman!" Look, when I shave every day, I don't look in the mirror and say, "Hey! There's a starship commander." [Laughs.] It's just not how I picture myself. So I was, like, "Really?" "Yeah, that's what they want."
And then I talked to Rick Berman, who was in charge of the whole Star Trek thing at the time, and he said, "Yeah, we figured that Harriman came from a wealthy, politically connected family, and they sort of bought you this job as a stepping stone into a political career." That was the backstory, which you never heard. All you knew was that there was this young, inexperienced guy who was given the Enterprise-B, which was ill-equipped. And it wasn't his fault. It was because half of the systems hadn’t been installed. But they decided to take it out for this PR stunt, a publicity run with three heroes, and nothing works, and of course he doesn't know what to do, so Kirk has to take over, after which Kirk gets sucked out into the Nexus, into a time warp, and it leads to his ultimate demise. So from that point on, half the people in the Star Trek world love me for killing Kirk, and half the people hate me for killing Kirk. And I can live with that.  
In early drafts of Star Trek Generations and various merchandise released before the movie, the commanding officer of the Enterprise-B was called "Harry Johnson."
In the Star Trek: The Next Generation Interactive Technical Manual, the computer refers to him as "James Harriman."
Captain Harriman and the Enterprise-B are featured in the 1995 novel The Captain's Daughter, in "Shakedown", a short story in the 2000 anthology Star Trek: Enterprise Logs (both of which were written by Peter David), and in the Star Trek: The Lost Era novels Serpents Among the Ruins and One Constant Star, both by David R. George III. He makes an appearance early in the first issue of the Star Trek: Spock: Reflections comic, showing Spock the place, now adorned with a dedication plaque, where Kirk was pulled into the Nexus – Harriman was distraught that he'd lost James T. Kirk on his first command, but Spock, reminding him of the 47 El-Aurians saved by the Enterprise, insisting that he had nothing to be ashamed of. Harriman featured prominently in the 2010 comic book issue Captain's Log: Harriman, detailing his struggle to overcome his guilt and his doubts in the aftermath of the shakedown cruise and Kirk's "death".
Serpents Among the Ruins gives his full name as John Jason Harriman II and that he was born aboard the USS Sea of Tranquility (β) and lived most of his childhood on a series of starships. Until his entrance into Starfleet Academy, he had never spent more than a few weeks planet side. This was an uncomfortable experience for Harriman as he found the sky in particular to induce agoraphobic reactions. But after a few months, he recovered and excelled in his studies. He studied the Romulan Star Empire in depth, an interest he had maintained after hearing stories of his grandfather's participation in the Earth-Romulan War as told by his father. He graduated in three years on an accelerated program. The novel also indicates that Harriman, working with Starfleet Intelligence, was the main architect of what became the Tomed Incident; the effort was intended to defuse tensions with the Romulan Star Empire by forcing them to stand down when the Klingons sided with the Federation after the Romulans destroyed a series of Federation border outposts. The outposts were revealed to be completely empty, with false sensor readings indicating life signs. After the signing of the Treaty of Algeron, Harriman steps down as captain of the Enterprise-B and turns it over to his first officer, Demora Sulu.
In One Constant Star, eight years later, Harriman is assigned as "admiral-at-large" of Helaspont Station, commanded by his wife, Captain Amina Sasine; they team up with Demora and the Enterprise-B to rescue Demora's father, Captain Hikaru Sulu, and the survivors of the destroyed USS Excelsior. This novel reveals that Harriman had a sister named Lynn who was murdered in 2275.
The short story "Full Circle" in the anthology book Strange New Worlds VII shows Harriman at the rank of admiral and serving as Starfleet Command's liaison to the Starfleet Corps of Engineers in 2371 – the year Kirk emerged from the Nexus and was killed on Veridian III. He turns the job over to Montgomery Scott, remarking that a real engineer could make something of the job – setting the stage for the Star Trek: Starfleet Corps of Engineers series. The Star Trek: Typhon Pact novel Raise the Dawn mentions that Harriman is still alive in the 2380s.
Harriman's mirror universe counterpart appears in the Star Trek: Mirror Universe novel The Sorrows of Empire, where he's a lieutenant assigned to the ISS Hornet in the 2270s and later attempted to transfer to the ISS Enterprise in 2275.
The personnel file created by Michael Okuda for the video game Star Trek: Starship Creator includes several connections to Ruck's role as Cameron Fry in the movie Ferris Bueller's Day Off, including a wife named Sloane and a son named Ferris who both live in Chicago, as well as an interest in 20th century Italian sports automobiles.