Both are heading to the NFL draft after leading the Knights to the most successful campaign in program history.
The players announced Monday that they will skip their senior seasons.
"After a lot of deliberations and talking with my parents, I've decided to try and pursue my goal to play in the NFL and capture my lifelong dream," Bortles said. "I just couldn't be more proud to say I played football at UCF, and it was the best four years of my life."
In his second year as the Knights' starter, Bortles helped UCF bounce back from a narrow early season loss to South Carolina to end the season on a nine-game winning streak capped by a 52-42 upset of heavily favored Baylor in the Tostitos Fiesta Bowl.
Bortles was a constant throughout UCF's run to its first BCS bowl, helping the Knights survive in seven games decided by seven or few points. It included a 21-point comeback in an upset win over then-top 10 ranked Louisville. The 12-1 record was a program best.
He finished 2013 passing for 3,581 yards and 25 touchdowns. The season followed a sophomore campaign in which he threw for 3,059 yards and 25 touchdowns.
Johnson, who transferred from Miami after his freshman season in 2010 and after sitting out in 2011, spent his first season at UCF backing up Latavius Murray. He was elevated to the starting job as a junior this season and finished with 1,139 yards and 14 touchdowns. He had three touchdowns against Baylor.
"This was a tough journey for me and I'm just super proud to have the support of Coach [George] O'Leary and the coaching staff," Johnson said. "It was a hard decision, but I had to make the best decision for me."
Bortles sought a rating from the NFL Draft Advisory Board and reportedly received a first-round grade. Scouts Inc. lists Bortles as the second quarterback (behind Louisville's Teddy Bridgewater) and 15th overall prospect.
Daunte Culpepper is UCF's highest-ever draft pick, having been taken 11th overall in 1999.
Not heavily recruited out of nearby Oviedo High School, Bortles redshirted his freshman year in 2010 and was Jeff Godfrey's backup as a redshirt freshman in 2011.
Godfrey initially flourished and was named Conference USA's freshman of the year in 2010 for leading the Knights to an 11-3 finish and Liberty Bowl win over Georgia. But he struggled during a 5-7 season in 2011 that saw Bortles appear in 10 games. Godfrey briefly left the team following that season and Bortles moved into the starting role. Godfrey returned to the program as a receiver.
Bortles' departure leaves a huge hole the Knights' offense, though they lose only seven scholarship seniors from this year's roster. Both quarterbacks behind Bortles on the roster -- Justin Holman and Pete DiNovo -- are freshmen.
Another freshman, William Stanback, is Johnson's likely replacement in the backfield.
Information from The Associated Press was used in this report.