The 55-year-old Ford took over as Sri Lanka's coach in 2012 for two years before moving to Surrey, whom he led to promotion from County Championship Division Two last year.
“Ford has been appointed with effect from Feb. 1,” a Sri Lanka Cricket source told Reuters without giving any further details.
The Sri Lanka head coach's position has been lying vacant since former test captain Marvan Atapattu resigned in early September.
Ford was South Africa's coach from 1999 to 2001 before moving to English county Kent as director of cricket in 2004. In 2006 he returned to South Africa to take charge of the Dolphins.
“We are extremely disappointed to be losing Graham Ford who has not just been an outstanding head coach but has played an integral role in the progress that we have achieved over the last two years,” Surrey director of cricket Alec Stewart said.
“He has worked tirelessly with the players and his efforts can be seen in their individual performances and the team's results, culminating in promotion back to the First Division.
“It was a very tough decision for Graham to leave Surrey but we understand that the opportunity to go back and coach at International level with Sri Lanka was too good to turn down.”
Original source: Ford returns as Sri Lanka coach