The 35-year-old joined NSW allrounder Steve Smith and West Indies offspinner Sunil Narine on Friday as additions to the defending champions' roster for the coming summer.
Lee, who retired from international cricket last week after returning home early from Australia's one-day tour of the UK with a calf injury, turned down a contract with NSW last month.
While he said he'd play limited-overs cricket with the Blues on a match-by-match-basis, Lee looks likely to restrict himself to just the BBL and Indian Premier League T20 tournaments.
Smith captained the Sixers last season and was recently named in Australia's squad for September's T20 World Cup.
Narine, 24, played under Sixers coach Trevor Bayliss at the Kolkata Knight Riders in the recent IPL competition, where he was player of the tournament, and was impressive in the one-day series against Australia earlier this year in the Caribbean.
His Windies teammate Kemar Roach, meanwhile, has penned a deal with the Brisbane Heat, who also snared batsman Peter Forrest and rising quick Cameron Gannon.
Days after being omitted from the Australia's one-day squad for their upcoming series against Pakistan in UAE, Forrest signed a two-season deal.
Forrest - currently serving as Australia A vice-captain on their tour of England - played for the Heat in the inaugural BBL, filling in as captain for six games for an injured James Hopes.
Roach - who has played 19 Tests and 67 ODIs for the Windies - has inked a one-season deal, becoming the Heat's second international import alongside Kiwi allrounder Daniel Vettori.
And James Pattinson's older brother Darren, a veteran speedster who has represented England in a sole Test in 2008, has signed a one-year deal with the Melbourne Renegades.