Chevron said the Alder project has already created hundreds of jobs across the UK, including in Aberdeen and Invergordon.
Gas produced from the field will be sent via a 17-mile (28km) pipeline to the ConocoPhillips-operated Britannia platform.
The Alder field was discovered in 1975.
Chevron said development was originally considered impossible due to the challenges of the field's reservoir, lying 14,700ft (4,480m) beneath the seabed.
The company said it was now viable due to the "right combination of technology, infrastructure for processing and export, and commercial conditions".
Chevron Upstream Europe managing director Greta Lydecker said: "First gas at Alder represents a significant milestone for Chevron and highlights our commitment to investing and developing resources in the UK.
"Alder supports our goal of helping maximize the economic recovery of the UK, adds significant production to our portfolio, and helps extend the field life of Britannia, an important asset to Chevron in the North Sea."
Deirdre Michie, chief executive of industry body Oil and Gas UK, said: "It shows the opportunities that are still out there."
She called for a "stable fiscal regime" to help boost investor confidence in North Sea exploration and production.

Metropolitan Police officers were sent to 166 key junctions during London's rush hour periods as part of Operation Safeway.
It follows the deaths of six cyclists in the city within a two-week period.
Between Monday and Wednesday 1,392 fixed penalty notices were issued to motorists and 755 to cyclists.
The force said the most common reason for motorists being stopped was for using a mobile phone while driving and jumping red lights.
Cyclists were spoken to for jumping red lights, cycling on the footway and having incorrect lights.
Additionally, 28 people were arrested for assault, possessing drugs, driving while disqualified, failing to stop and assaulting a police officer.
Ch Supt Glyn Jones said: "This operation is aimed at getting all road users to behave more safely on the roads, for their benefit and the benefit of others.
"My hope is that as the operation continues, compliance with the law and the highway code will improve and the need to issue fixed penalty notices will diminish."
During the operation, which will run until Christmas before being reviewed, 2,500 officers will hand out advice to anyone seen putting themselves or other road users and pedestrians at risk.
The six cyclists who died between 5 and 18 November are: Brian Holt, 62; Francis Golding, 69; Roger William De Klerk, 43; Venera Minakhmetova, 24; a 21-year-old man from St John's Wood and a man believed to be in his 60s.
The names of two of the victims have not yet been officially released by police.
Gas production has started from a North Sea field first discovered more than 40 years ago when its development was considered "impossible".
[NEXT_CONCEPT]
More than 2,000 fixed penalty notices were issued to motorists and cyclists during the first three days of a police road safety operation across London.