The Pars have announced they will confirm the appointment of a new boss at 12.30pm.
The announcement follows several days of negotiations with Jefferies and chairman John Yorkston told STV on Tuesday: "Jim has signed a contract with Dunfermline."
Jefferies, 61, has been out of work since being removed from his position as Hearts manager three games into the season, despite leading them to third place in the Clydesdale Bank Premier League last year.
The length of contract was thought to have been a stumbling block to a deal with Yorkston having admitted he would be happy with a short-term option. However, he hinted Jefferies had signed a longer deal.
Jefferies has eight games to bridge a four-point gap on Hibernian to save the Pars from relegation from the SPL. His first game comes against St Mirren on Saturday, where Dunfermline are seeking their first home win of the season, and the Fifers then face Dundee United and Hearts before the league splits.
Meanwhile, midfielder Gary Mason believes staying up would be a tribute to Jim McIntyre, who was sacked on Friday.
"For one reason or another as players we have not produced, but with three games to the split, eight games in total we will give everything," the 32-year-old said on the club's official website.
"The manager never made excuses. All right, we might have had injuries but we need to deal with that situation.
"He has built up this squad over the four and a half years that he has been here and for us to stay up would be the greatest tribute. As players we want to go and finish the season on a high."