Convey spent the past three seasons with the Earthquakes, appearing in 75 games and scoring three goals while adding 14 assists.
"Bobby Convey has been a difference-maker in this league for many years, with experience at the highest levels of soccer," Sporting Kansas City manager Peter Vermes said. "His competitiveness and attacking qualities stand out and we feel that he can thrive within the culture created at Sporting Kansas City. We are very excited to welcome Bobby to our club."
The 28-year-old joined D.C. United when he was 16 and went on to play in 72 matches for the club before moving to England to play for Reading.
"I am very excited to link up with my new club and teammates," Convey said. "The fans in Kansas City are extremely supportive of the team and create a great atmosphere in the new stadium. The team proved last year they are a good team that can win a bunch of games and I hope I can add to that success."