The defender's contract was set to expire in the summer and Orlando City was not expected to pay a fee to acquire his services.
“Lamine will significantly strengthen our back line,” Orlando City general manager Niki Budalic said in a club statement.
“He brings tremendous experience at the highest levels of European football and we believe he will fit right in with what we’re trying to build in Orlando.”
Sane made 38 total Bundesliga appearances in 2016-17 and 2017-18 with Bremen, scoring two goals and adding one assist.
The Senegal international was an undisputed starter for the club in 2016-17, before losing his grip on a starting spot this season.
The center back has been capped 25 times by the Senegal national team, which is one of five African nations to qualify for the 2018 World Cup.