FIFA had already announced in March that the final would be played on December 18 -- Qatar's national day -- and the start date confirmed on Friday means the tournament will run for 28 days, four days shorter than usual.
The tournament, usually played in June and July, was moved to avoid the effects of the searing desert heat in the Gulf at that time of year.
The decision to award Qatar the hosting of the tournament, taken in 2010, along with that of the 2018 tournament to Russia has been the subject of a Swiss investigation centred around whether bribes were paid during the bidding process.