Dundee's draw with Queen of the South meant Ross County were promoted to the Scottish Premier League.
Dundee needed to win to delay County's First Division title celebration, but Queens defender John Potter cancelled out Stephen O'Donnell's opener in the 82nd minute for a 1-1 draw.
O'Donnell opened the scoring with a deflected strike from long range in the 53rd minute at Dens Park, but his former St Mirren team-mate Potter headed home Daniel Carmichael's cross following a half-cleared corner.
The draw left Dundee 14 points behind the leaders with four games left.
Ross County have five games remaining and face Ayr United at Somerset Park on Wednesday night.
The former Highland League side, who were admitted to the Scottish Football League in 1994, will make their SPL debut next season.
But they have already made their mark at the highest level by reaching the 2010 Scottish Cup final, where they lost to Dundee United.