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 today 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.
"That will include a single league body, subject to club consultation."
League places would be based on sporting performance and no club would be fast-tracked to a higher level, sources close to the talks said, meaning that there would be no short cut for Rangers.
"We will deliver the change, as a collective, when we believe it's the right time for the game" - SFA's Stewart Regan
Regan added: "The next stage is to take a worked-up plan to clubs and we hope to do that by the end of January."
Regan, who was accompanied by SPL chief executive Neil Doncaster and SFL counterpart David Longmuir, confirmed the proposals being examined would see the two top divisions split into three groups of eight after 22 games.
Regan added: "Ultimately it will be the clubs that decide but we have seen today a willingness to make change happen and a recognition that Scottish football is crying out for a new dawn and we have now got agreement to take to clubs for a single league body.
"That is a huge step for the game in Scotland and it shouldn't be underestimated.
"The clubs will decide what can be delivered by the start of the coming season, but that's not something we are going to get hung up on.
"We will deliver the change, as a collective, when we believe it's the right time for the game."
The top 12 clubs broke away in 1998 but a single body now appears inevitable.
Doncaster said: "What's important is that we focus on what is wanted by the game, which is a single league for the benefit of all 42 clubs; a structure that benefits, particularly clubs in the second tier, so that the financial problems faced by clubs being relegated are alleviated; that we ensure a pyramid for the whole game; that we ensure proper governance structure.
"All of these things are the fundamental building blocks that we will work towards.
"The detail we will have to work through but that's for another day."
Longmuir argued Scottish football was better served by one league body.
He added: "I was hugely encouraged by today because we need to get the pillars of the game back in solid foundation.
"The governance of the game and distribution of wealth will now affect all 42 clubs, and I think that in itself is a major breakthrough.
"Every club should be able to embrace this because they are all going to benefit from it.
"Hopefully we can get the fans and let them engage with the process as well because what we are doing in the foundations of the game - distribution, governance, play-offs, more meaningful games, a pyramid - those are the key things."
The SPL needs an 11-1 majority to push through the plans but already had a unanimous agreement in principle on the plans.
The SFL, which had previously backed a 16-10-16 plan, needs a minimum 75 per cent agreement.
No short cut for Rangers
Former champions Rangers will not be offered a short cut back to the top of Scottish football under the plan.
Rangers have had to relaunch from the lowly fourth tier of the Scottish game after collapsing under a pile of debt last year.
The demise of the 54-times champions has added to the financial problems facing many clubs in Scotland where attendances are modest for most teams except Rangers and Glasgow rivals Celtic.
Rangers said they were disappointed not to have been party to Tuesday's talks.
"It seems odd to us that as the biggest club in Scotland we were not invited to the meeting and there are many people who feel that change should not be rushed through for the sake of it," the club said in a statement.
"We have said consistently that we have not made any plans based on being fast tracked through the leagues in a reconstruction process," Rangers added.
Rangers are proving too strong for the current 10-team Scottish Third Division which they lead by 17 points.