Both Scottish league bodies have agreed in principle to a restructuring plan that would see the organisations merge in a 12-12-18 structure.
Both sets of clubs have still to vote on the proposals but a major breakthrough was made during a meeting of the main decision-makers in the Scottish Premier League, Scottish Football League and the Scottish Football Association.
SFA chief executive Stewart Regan said: "We have had a very productive meeting of the Scottish FA's professional game board at which we had board representatives from around a third of the 42 senior clubs in Scotland. I'm delighted to say that we have agreed a set of principles to restructure Scottish football."
Regan added: "That will include a single league body, subject to club consultation."