The midfielder completed a move from Aston Villa on Sunday.
The winger completed a move to the Scottish champions on Sunday, signing a four-year deal at the club.
He becomes their fourth signing of the summer transfer window, following Kolo Toure, Kristoffer Ajer and Moussa Dembele in making the move to Celtic Park.
The move sees him reunite with former manager Brendan Rodgers, who he previously worked with at Swansea City.
It is hoped he can add quality to a Celtic forward line that relied heavily on Leigh Griffiths last season, and Celtic fans are pleased with his arrival.
Absolutely buzzing Sinclair, great signing. Can't wait to see him play! Exciting season ahead— Muireann Fanning (@muireannf) 7 August 2016
Scott Sinclair is the kind of signing we need. Hopefully he can produce his best football in the hoops. Welcome to Celtic— Ewan (@ewanmac5) 7 August 2016
Celtic summer signing— Fitzy (@Fitzy_07) 7 August 2016
All Champions League quality (in my humble opinion)
Roberts, Griffiths, Dembele & Sinclair— Hez (@Hez_cfc67) 7 August 2016
Scott Sinclair, Paddy Roberts, Griffiths & Dembele— Paul (@Paulmcc67) 7 August 2016
Roberts, Sinclair, Dembele & Griffiths - great attack! ⚽️— Stephen Miller (@94stephenmiller) 7 August 2016
Scott Sinclair, welcome aboard. Excited to see what he can bring to the team.— Maley's Bhoys (@MaleysBhoys) 7 August 2016
Scott Sinclair is an excellent piece of business by Brendan— Martin Rodgers (@MartinRodgersXV) 7 August 2016
It now remains to be seen if Sinclair can get his career back on track after it has stalled over the last few years.
He failed to find regular game time at Manchester City among their plethora of stars, while at Villa he struggled to find his best form in a team that was eventually relegated from the Premier League.
He has previously shone under Rodgers though and he will be hoping that he can do so again in the Scottish Premiership.