After being picked with one of the last picks of the 2015 NFL Draft, Trevor Siemian would spend three seasons with the Denver Broncos. In Siemian's first season, he was the backup for future Hall of Famer, Peyton Manning. Before the 2016 season, Siemian would beat out Paxton Lynch and Mark Sanchez for the starting job.

In 2016, Siemian started 14 games for the Broncos, throwing for 3,401 yards and 18 touchdowns on 59.5% completion. Siemian's best game that year was a loss to the Kansas City Chiefs, where he threw for 368 yards and three touchdowns while completing 20 of his 34 pass attempts.

Siemian would win the Broncos' starting job again in 2017 and started 10 games that year for Denver, where he threw for 2,285 yards and 12 touchdowns, completing 50 percent of his passes. Siemian also showed some mobility that year, running for 127 yards and a touchdown on 31 carries.

In the 2018 offseason, Siemian was traded to the Minnesota Vikings where he would serve as the backup to Kirk Cousins for the entirety of the 2018 season.