The project should create more than 700 jobs, with 200 posts onshore in Aberdeen and 500 offshore.
Mariner, about 90 miles east of the Shetlands, was discovered in 1981 and is thought to contain 2bn barrels of oil.
It had not been exploited to date because it is “heavy” oil, which flows less easily from the rocks and so is more expensive to extract.
Technological advances and higher oil prices have since helped to make such developments economic.
Statoil entered the Mariner licence in 2007 “with the aim of finally unlocking the resources” but suspended work in March 2011 after George Osborne’s surprise windfall tax on North Sea oil and gas, which it said significantly affected its economics.
It only resumed work after the Treasury subsequently made tax concessions.
Lars Christian Bacher, executive vice president of Statoil, said: “We are satisfied that we now are able to make an investment decision for a profitable development of the Mariner field.”
Statoil said it should be able to extract more than 250m barrels of oil from the field, with first production in 2017, subject to regulatory approval. Output should be 55,000 barrels per day for the first four years before slowing down and the field should produce for 30 years.
Mike Tholen, economics director of industry body Oil & Gas UK, said: “Close work between the industry and Treasury and recent changes to the tax regime to boost investment in the UK’s oil and gas reserves have also been instrumental in allowing difficult projects like these to go ahead.
“The more UK oil and gas reserves are developed, the greater the boost to jobs and the public purse.
“The economic benefits of such developments for the whole of the UK and the huge remaining potential 24bn barrels - are a stark reminder of the importance of ongoing engagement with the Government to further improve the oil and gas business environment."