Ex-Arsenal striker Park Chu-young gave FC Seoul a 1-0 win at the home of South Korean title rivals Jeonbuk Motors on Sunday to clinch the title on the final day of the K-League season.
With the teams locked on points before kick-off, Seoul, who had scored less goals over the season, had to win.
Park, who played just seven minutes in the English Premier League for Arsenal from 2008 to 2011, scored in the second half.
Jeonbuk, going for a third successive title, had been 14 points clear with six games remaining but was docked nine points in September after a club scout was convicted of bribing referees in 2013.
Jeonbuk takes on U.A.E team Al Ain in the final of the Asian Champions League later in November.