Calum Waters has agreed a new contract at Kilmarnock until 2021, but will remain on loan at St Mirren until the end of the season.
The 23-year-old left-back made 18 appearances for the Buddies in the first half of the campaign.
Killie confirmed the news on their official website and wished the player “all the best for the rest of the season”.
Waters, who started his career at Celtic, signed for Kilmarnock from Alloa in June, 2017.
Meanwhile, Killie later lost Liam Millar after Liverpool recalled the forward from his loan spell.
The 20-year-old Canada international first joined the Ayrshire club a year ago and returned for a second stint at the start of the season.
His winner against St Mirren in Paisley last March helped Killie to a third-place finish in the Ladbrokes Premiership.
A statement on Kilmarnock’s official website read: “We can confirm that Liam Millar’s loan spell with Kilmarnock has ended, with Liverpool recalling the forward back to Merseyside with immediate effect.
“Liam first joined the club in January 2019, and played his part in securing our highest league finish in 50 years: scoring a memorable late strike against St Mirren in March.
“We would like to place on record our sincere thanks to Liam for his contributions to Kilmarnock, and wish him every success in his future career.”