The left-armer will remain at Hove until the end of the 2015 season.
Liddle, 29, joined Sussex in 2006 after starting his career at Leicestershire and is key part of the county's limited-overs side.
"I'm delighted to have signed for another two years with Sussex," he said.
"I've had a good last couple of seasons, particularly in Twenty20 and I'm determined to continue that form and hopefully help the team progress further.
"We want to be challenging for trophies every season in all formats of the game and I want to keep contributing by taking wickets and helping the team win matches."
- Sports & Recreation