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By 2369, O'Brien had been operating transporters for 22 years. O'Brien, promoted, transferred to Deep Space 9 as chief of operations.
(DS9: "Emissary")

Not long after, O'Brien received a note on his record for violating the Prime Directive, after assisting in the escape of a Tosk disobeying orders from Commander Sisko.
(DS9: "Captive Pursuit")

He later found himself entangled in local Bajoran politics when he visited a remote village on the planet.
(DS9: "The Storyteller")

In 2369, O'Brien's assistant Neela attempted to assassinate Vedek Bareil.
(DS9: "In the Hands of the Prophets")

He assisted Kira Nerys in rescuing Li Nalas from a Cardassian labor camp.
(DS9: "The Homecoming", "The Circle", "The Siege")

In 2370, O'Brien was assisting the T'Lani and Kellerun militaries in disarming and neutralizing their harvester weapons when a sabotage attempt exposed him to deadly nanobiogenic gel. He was saved by Julian Bashir, an act which developed their friendship
(DS9: "Armageddon Game", "Whispers")

Later in 2370, Quark tried to use Bashir and O'Brien in a racquetball scam.
(DS9: "Rivals", "Paradise")

O'Brien was arrested by Cardassian forces and put on trial for allegedly supplying weapons to the Maquis.
(DS9: "Tribunal")

In 2371 O'Brien helped disable a self-destruct mechanism on the station left by the Cardassians.
(DS9: "Civil Defense", "Past Tense, Part II", "Destiny")

When the Klingons attacked and invaded Deep Space 9 in January of 2372, O'Brien defended Ops against boarding parties, suffering minor injuries in the attack.
(DS9: "The Way of the Warrior")

His image was accidentally used in a holo-program by Julian Bashir and Garak when a runabout he was on was destroyed by Cardassian terrorists.
(DS9: "Our Man Bashir")

Falsely accused of spying Miles was temporarily relieved of his duties by Captain Sisko, following a visit to the planet Argratha.
(DS9: "Hard Time")

In late 2372, O'Brien commented that his career had included service on half a dozen ships.

In 2373, O'Brien took part in an infiltration mission to the fortified Klingon moon of Ty'Gokor.
(DS9: "Apocalypse Rising")

O'Brien, as part of a Defiant away team, discovered a crashed Jem'Hadar ship on a planet.
(DS9: "The Ship")

On an assignment to Empok Nor to get a part necessary for the station, he and his team found two Cardassians in stasis.
(DS9: "Empok Nor")

O'Brien was partly responsible, along with Rom and Jadzia Dax, for creating and deploying the self-replicating minefield that blocked Dominion ships from entering the Alpha Quadrant, an event which precipitated the Dominion War. (DS9: "Call to Arms")

Along with the rest of the DS9 command crew, O'Brien was pulled from front-line duty to take a captured Jem'Hadar vessel behind enemy lines. (DS9: "A Time to Stand")

He was part of the away team that confronted the Jem'Hadar on a planet after both sides crashed.
(DS9: "Rocks and Shoals")

Following their rescue by the Rotarran, Miles took part in Operation Return, which successfully recaptured the station. He resumed his duties aboard the newly-retaken Deep Space 9.
(DS9: "Sacrifice of Angels", "You Are Cordially Invited")

In mid-2374, O'Brien was recruited by Starfleet Intelligence to infiltrate the Orion Syndicate arm on Farius Prime.
(DS9: "Honor Among Thieves")

He helped rescue the Defiant after it had been taken over by the Jem'Hadar. (DS9: "One Little Ship", "Time's Orphan")

Following the death of Jadzia Dax at the end of 2374, O'Brien took part in the Rotarran's successful assault on the Monac shipyards.
(DS9: "Shadows and Symbols")

Later in 2375, Miles disappeared on New Sydney while attempting to track down Morica Bilby, Liam's wife, who had disappeared from her home on the planet.
(DS9: "Prodigal Daughter")

Shortly before the final battle of the war, O'Brien took part in the attempt to restore Vic Fontaine's casino.
(DS9: "Badda-Bing, Badda-Bang")

Shortly before the end of the war, O'Brien accepted a position at Starfleet Academy as a professor of engineering.
(DS9: "What You Leave Behind")