The First Minister is in the driving seat to beat Alistair Darling, leader of the pro-UK Better Together organisation, in the special STV programme, which is expected to be watched by hundreds of thousands of people.
Bookmakers are offering odds as low as 1/2 on the SNP leader outscoring his main opponent in the two-hour showdown in the Royal Conservatoire in Glasgow.
However, the debate comes as William Hill is offering 1/7 on a vote against independence, their lowest price yet, and 4/1 on a Yes vote on September 18. It followed a fresh spate of bets for the No vote, including an online wager of €12,000 (£9552).
The broadcast comes two days after the closing ceremony of the Commonwealth Games. Campaigning by the main leaders was almost non-existent during the Games.
Yes Scotland chief executive Blair Jenkins said Mr Darling's low popularity in approval polls compared to Mr Salmond would count against him tonight.
The No camp believes the broadcast is a chance for people to question Mr Salmond on issues such as the future of the pound.
Yes supporters hope that, with six weeks' campaigning remaining, it will be a game-changer, after a weekend poll showed little movement in support for either side. Pollsters Survation put Yes on 40 per cent, down one point compared to the previous month, while support for a No vote was unchanged on 46 per cent.
The bookies will use forthcoming opinion polls to judge the result of the debate, as the 350-strong invited audience will not be asked to provide a snap verdict on the night.
Bookmaker McBookies offered odds of 6/4 on a victory for Mr Darling, with Ladbrokes quoting 7/4.
Mr Jenkins said: "Independence is the opportunity of a lifetime for the people of Scotland, and the Yes campaign are looking forward immensely to the debate. Our experience is that most undecided voters choose Yes when they hear both sides of the debate, and therefore we believe the mass TV audience will benefit our positive campaign.
"We also believe that the No campaign have a problem with both the negativity of their message, and the unpopularity of their messengers.
"The Yes leaders all have positive ratings because they are trusted, and the No leaders' ratings are all negative."
The Yes campaign highlighted approval ratings which showed Mr Salmond had a positive score of five.
Blair McDougall, the campaign director of Better Together, said: "Voters in Scotland have been listening to the independence debate for over two years now. Surely if Alex Salmond had convincing answers on the details of separation, we would have heard them by now.
"Scots tuning in deserve to finally get straight answers from Mr Salmond to the questions they have been asking."
There will be roughly equal numbers of Yes and No supporters in tonight's audience, with around 20 per cent said to be undecided.
Former William Hill chief executive Ralph Topping, who used to commute from Scotland to his London office, has said he is backing the Yes campaign.