The Owls (10-3) relied on their bruising ground attack to subdue the Herd (9-4), with running backs Charles Ross and Luke Turner delivering via versatility. Rice gained 250 of its 489 yards on the ground.
After the game, Rice accepted a bid to the Liberty Bowl, while Marshall will head to the Military Bowl.
Ross rushed for 109 yards and two touchdowns, upping his season total to 14 and matching the program single-season mark set by Trevor Cobb in 1991. Turner passed for two touchdowns, doubling his career total.
The Owls' defense was exceptional, limiting the Herd to 371 yards and just 4.8 yards per play. Marshall averaged 53 points during the five-game winning streak it carried into its first C-USA Championship Game appearance.
Herd quarterback Rakeem Cato passed for 265 yards and two touchdowns in the loss.
The Owls stuffed Marshall tight end Devon Johnson on fourth down with 8:59 left to play. Two plays later, Ross rumbled in for a 16-yard touchdown that capped the scoring and the Owls' first C-USA crown.
Rice scored on its opening possession for the 12th time this season, covering 82 yards over 10 plays in grabbing a 7-0 lead. The Owls' effective run-pass mix set the stage for a trick play that culminated the march, with Turner completing a 35-yard halfback pass to Donte Moore for a touchdown at the 10:15 mark of the first quarter.
Rice opened the drive with three consecutive pass attempts and followed with four successive run plays. When Turner took the halfback toss from quarterback Taylor McHargue, the Herd secondary advanced to fill running lanes and lost coverage, leaving Moore with an open expanse to the end zone.
Rice was less methodical on its second possession, with McHargue and Jordan Taylor teaming on a 75-yard score on the second snap. That pass play was the longest in C-USA championship game history and represented a career long for Taylor, who completed the half with 131 yards.
Marshall, meanwhile, struggled to get its prolific offense rolling. The Herd managed only 58 yards in the first quarter and closed its opening two possessions with punts. Its initial scoring drive covered 64 yards yet required a dozen plays and eventually bogged down at the Rice 9.
The Herd, the league leaders in total offense (513.2 yards per game) and scoring offense (44.6 points per game), settled for a 27-yard field goal from Justin Haig that cut the deficit to 14-3 with 12:21 remaining in the half. Marshall managed to complete its ensuing possession with a 1-yard Devon Johnson touchdown run at the 9:18 mark of the second quarter, but that followed a brisk 4-play, 62-yard touchdown drive by the Owls.
Rice surprised Marshall with a hastened pace in extending to a 21-3 lead, catching the Herd flat-footed in the process. McHargue opened with pass plays of 28 and 20 yards to Darrion Pollard and Taylor before Ross covered the final 14 yards on the ground, including a bruising 4-yard scoring run just 52 seconds after the possession began.