9 March 2017 04:35 pm
The 31-year-old leg-break bowler played 11 times in the competition for Northants last season, taking 12 wickets at an average of 24 runs.
Prasanna has appeared in 34 one-day and 14 Twenty20 internationals, including February's series against Australia.
"The more match-winners on your teamsheet the better," head coach David Ripley told BBC Radio Northampton.
"It's his consistency with the ball, he's been bowling the power-play against Australia and doing a good job of that.
"There's some Sri Lankan cricket but at this stage it looks like he can pretty much do the whole competition, which is positive for continuity."(BBC)