Collins had an 82-yard scoring run and touchdown catches of 52 and 4 yards, and Jordan Wells had 10 tackles, including six for losses, on a defense that held Gilmer to 162 total yards.
Navasota (16-0) won its first state championship in its second title game appearance. Navasota lost to Southlake Carroll in Class 3A in 1988.
Gilmer (13-2) actually led 3-0 on a 29-yard field goal by Pablin Olivares in the first quarter. But Collins scored on the 52-yard completion from Kadarius Baker less than two minutes later to put Navasota in front for good.
Gilmer was seeking its third state title since 2004.
After Collins' first touchdown, Baker's scoring plunge from 2 yards gave Navasota a 10-point lead, and Derrion Randle followed with a 52-yard run for a 20-3 lead.
Trailing 26-3 in the third quarter, Gilmer drove 45 yards in 16 plays to the Navasota 2. On fourth down from there, quarterback Tanner Barr lost control of the ball as he stretched for the goal line, and the fumble went through the end zone for a touchback.
Three plays later, Collins was at quarterback when he took the snap and sprinted 82 yards for a 33-3 lead.
Baker was 8 for 13 for 123 yards for Navasota.