Royster made his college football debut on September 1, 2007 against the FIU Golden Panthers. He played a significant role in the Penn State offense for the 2007 season. He was the second leading rusher behind Rodney Kinlaw, rushing for 513 yards on 82 carries for a 5.3 yards per carry average. He scored the game-winning touchdown in the third quarter of the 2007 Alamo Bowl against the Texas A&M Aggies.

Royster made his season debut against the Coastal Carolina Chanticleers on August 30, 2008 at Beaver Stadium. Royster and the offense helped guide the Nittany Lions to a 66-10 defeat of Division I FCS Chanticleers. Royster saw limited action in the rout. He had 64 yards on 8 carries for a career-high 3 touchdowns. Royster was pulled from the game following his third touchdown at the beginning of the third quarter when Coach Paterno sat all his starters in favor of the backups.

On September 6, 2008, against the Oregon State Beavers, Royster put up 141 yards on 17 carries. He added 3 touchdowns in the 45-14 blowout win before being taken out of the game. He was named the Big Ten Co-Offensive player of the week.

Royster had his second straight 100-yard game against the Syracuse Orange on September 13, 2008. He gained 101 yards on 13 carries in the 55-13 victory.

On October 25, 2008, Royster rushed 19 times for 77 yards in Penn State’s game against Ohio State. He tacked on 20 receiving yards on 3 catches in the Nittany Lions’ 13-6 triumph. The win against the then 9th-ranked Buckeyes was Penn State’s first victory at The Horseshoe since 1978.

On November 15, 2008, the Nittany Lions squared off against the Hoosiers of Indiana University. Royster rushed for 63 yards on 12 carries in chilly, rainy atmosphere of Beaver Stadium. Bouncing off three tacklers, he added his 11th rushing touchdown of the year on a 19-yard run in the third quarter. After leading 10-7 at the half, Penn State pulled away for a 34-7 victory.

Royster became the second player in Westfield Bulldog football history to have his jersey retired. The Bulldogs retired Royster’s #24 jersey during halftime of a 2012 game when the Bulldogs went up against Fairfax High School Rebels. Royster’s #24 was second to Eddie Royal’s #5 when Royal had his jersey retired in 2009 when the Bulldogs went up against the Chantilly High School Chargers.

Royster was selected to play in the 86th East-West Shrine Game played on January 22, 2011, at the Citrus Bowl Stadium in Orlando, Florida.

Royster was drafted 177th overall in the 2011 NFL Draft by the Washington Redskins. He was expected to compete with former Redskins’ running back, Ryan Torain, and fellow 2011 Redskins’ draftee, Roy Helu, but Royster did not make the 53-man roster and was cut on September 3. On September 4, 2011, Royster was signed to the practice squad. He was elevated to the Redskins active roster on November 22, 2011 when the Redskins waived Tashard Choice following Tim Hightower’s season-ending injury. In Week 12 against the Seattle Seahawks, Royster made his NFL debut. Royster would have his first career start in Week 16 against the Minnesota Vikings, getting 132 yards on only 19 carries. In Week 17 against the Philadelphia Eagles, Royster recorded 113 yards on 20 carries while suffering rib injuries. At the end of his rookie season, Royster recorded 328 yards on 56 carries making him the second leader in rushing yards behind fellow rookie, Roy Helu, and beating the original starting running back, Tim Hightower.

Royster was expected to compete for the starting spot in the 2012 season against Roy Helu and Tim Hightower, but lost the competition to rookie Alfred Morris. Before starting the season, he changed his jersey number to 22, his college jersey number. He scored his first career touchdown in Week 9 against the Carolina Panthers. In the Week 15 win over the Cleveland Browns, he would score his second career touchdown.

The Redskins released Royster on August 30, 2014 for final roster cuts before the start of the 2014 season, losing the third-string running back position to former Penn State teammate, Silas Redd.

On May 30, 2014, Evan married his longtime girlfriend Jaclyn McDonald. Evan is the younger brother of former Parade All-American and Stanford wide receiver Brandon Royster. He is also the younger brother of Cosmo’s 2008 Virginia Bachelor Kyle Royster.

Royster signed with the Atlanta Falcons on August 16, 2015. He was waived/injured by the Falcons on August 26, 2015. On the following day, he cleared waivers and was reverted to the Falcons’ injured reserve list. On September 1, 2015, he was released by the Falcons with an injury settlement.