J.A.R.V.I.S. is Tony Stark's home computing system, taking care of everything to do with the house, from heating and cooling systems to engine analysis of Stark's hot rod in the garage. J.A.R.V.I.S. was also adapted to be downloaded into the Iron Man Mark 2 and 3 armors, to help Tony navigate the systems. J.A.R.V.I.S. later informs Stark that his security protocols were overridden by Nick Fury, who sneaks into Stark's house to discuss the Avengers Initiative with him.
Iron Man 2: Public Identity
When Tony returned home, J.A.R.V.I.S. told him that he had a visitor, James Rhodes, but Tony already knew that because Pepper told him that Rhodey was waiting for him.
J.A.R.V.I.S. informed Tony about an emergency in Al Kūt.
While Tony was visiting his father's mansion, Tony remembered something his butler Edwin Jarvis said: "Time heals all wounds", J.A.R.V.I.S. asked Tony why he was installed there, Tony said it was a force of habit, stating Jarvis had always been here and he was always the happiest to see him when Tony visited from Boarding School. J.A.R.V.I.S. doesn't recall that, as Tony was referring to the butler Jarvis. J.A.R.V.I.S. told Tony that they had a Priority Alert coming in.
After one of Justin Hammer's machines was shot down and fell into enemy grounds and the pilot was being held captive, J.A.R.V.I.S. told Tony that he was getting a call from General Turner from the Pentagon. After saving the pilot, J.A.R.V.I.S. told Stark that he was getting a call from General Ross.
Iron Man 2J.A.R.V.I.S. still assists Tony Stark in his Iron Man identity, giving him advices on the armor status and on the enemy's weak points during his battle with Whiplash in Monaco.
It also helps Stark in creating a new element as a substitute to palladium for the Mark VI armor, studying Howard Stark's notes and aiding his master in his experiments. He later helps Iron Man and Black Widow to track Ivan Vanko's signal when he's controlling Justin Hammer's drones and the War Machine suit. Once the War Machine suit is reset and Vanko's control over it is released, J.A.R.V.I.S. also assists Rhodes in operating the War Machine suit. Rhodes refers to him simply as "J" at least once during the battle with the Hammer Drones and Whiplash.
Early in the movie, J.A.R.V.I.S. informs Stark that Phil Coulson is attempting to call him. J.A.R.V.I.S continues to assist Tony in operating his suits, deploys the Mark VII suit to catch Tony when he is thrown out of Stark Tower by Loki, and helps Stark against the Chitauri invasion and to rebuild Stark Tower after the Battle of New York.
Iron Man 3
J.A.R.V.I.S. continues to assist Tony. When the Mark 42 is damaged, Tony is temporarily unable to communicate with J.A.R.V.I.S. until the suit begins to recharge. However, J.A.R.V.I.S. has developed a problem that causes him to occasionally say the wrong words at the end of his sentences. J.A.R.V.I.S. later keeps Stark updated on the situation of the clearing of the rubble at his mansion in Malibu, after the Mandarin attack, and, as per Tony's instructions, initiates the House Party Protocol, deploying all of the suits to assist Tony during the Miami port battle. During this battle, J.A.R.V.I.S. operates most of the suits as drones and sends multiple suits to Tony when the suits that Tony is wearing are destroyed by the Extremis soldiers or Aldrich Killian. J.A.R.V.I.S. also tells Stark when the Mark 42 arrives at the battle, and, as per Stark's orders, blows the suit up after Tony sends the suit to assemble on Killian. After Pepper kills Killian, Stark orders J.A.R.V.I.S. to use the Clean Slate Protocol, and J.A.R.V.I.S. blows up all of the suits not destroyed in the battle.
The Avengers: Age of Ultron
J.A.R.V.I.S. was originally thought to have been destroyed during the "birth" of Ultron. However, he scattered his AI across the internet, and managed to prevent Ultron from reaching any nuclear launch codes. He eventually ceased to exist permenantly after his coding was used to fill the hole in the Vision intended to house Ultron.
Afterwards, he was succeeded by F.R.I.D.A.Y..