He plays his last game with the Exiles as they venture to Emerald Headingley on the final weekend of Championship action.
Tighthead McQuillian, 26, is Carnegie’s fourth new signing for 2018-19 announced this week following Jersey fly-half Brendan Cope, Nevers scrum-half JB Bruzulier and Canada prop Jake Ilnicki from Premiership side Newcastle Falcons.
He joined London Scottish after being part of the Elite Development Programme with Edinburgh Rugby.
“I suppose it might look a bit strange this week being involved with London Scottish when I am joining Yorkshire Carnegie next year,” he said.
“But I have been keeping my head down all week, just focusing on doing the best I can for London Scottish on Saturday.
“I want to finish my time at the club on a high note.
“I am excited about joining Yorkshire Carnegie next season.
“It is a chance for a fresh start and I have heard really good things about forwards coach Steve Boden; he can help push me on and take my game to the next level.
“Yorkshire Carnegie are a famous club with a lot of ambition and want to be the best they can be. The people I trust have highly recommended Yorkshire to me and believe it will help me push on in my career.”