Walker played high school football as well as baseball and track and field at Hillsboro High School. He also participated in power-lifting. He was named an honorable mention to the 2008 Super Centex team and a member of the 2009 All-Centex team by the Waco Tribune-Herald. From 2010 to 2011, he played junior college football at the local Trinity Valley Community College. During his two seasons at Trinity Valley, he made 44 catches for 864 yards and 10 touchdowns while helping to lead his team to the second round of playoffs in 2011. Walker committed to transfer to Texas A&M in early 2012 to play for the Aggies. In a fall scrimmage, Walker caught two touchdown passes of 20 and 35 yards. He played a minor role in the regular season, playing in 12 games but catching only eight passes for 85 yards and no touchdowns. Walker was more active in his final year with the Aggies in 2013. He played large roles against Arkansas when he caught seven passes for 81 yards and against Vanderbilt when he caught his first two touchdown passes at Texas A&M. Walker was third on the team in catches with 45 receptions and second on the team with 705 receiving yards in the regular season. In the post-season, Walker made an impact at the Chick-fil-A Peach Bowl, where he made six catches for 113 yards including a 44-yard touchdown. He finished his career at Texas A&M with finishing with 59 receptions for 903 yards and five touchdowns. Walker was the last receiver to catch a pass from quarterbackJohnny Manziel before Manziel was drafted by the Cleveland Browns.
Walker was eligible for the 2014 NFL Draft but went undrafted. He was later signed by the Tennessee Titans as a free agent. He was released at the end of the pre-season in 2014.
Walker was signed as a free agent by the Edmonton Eskimos on April 29, 2015 after participating in an Eskimos mini-camp in Florida. He was placed on the practice roster at the end of the pre-season, where he remained until he was activated in early August following a hip injury to Adarius Bowman. Walker made his CFL debut in a game against the Montreal Alouettes on August 13, where he recorded 10 catches for 125 yards as well as a tackle. The following week against the Hamilton Tiger-Cats, Walker caught 14 passes for 183 yards. Walker would go on to finish the 2015 CFL season with 89 receptions and 1,110 yards and 6 touchdowns. In the Western Final, Derel Walker had 11 receptions for 125 yards and a touchdown as the Eskimos advanced to the 103rd Grey Cup game over the Calgary Stampeders, their provincial rivals. During the Grey Cup festivities, Walker was named the CFL's Most Outstanding Rookie. Walker continued to perform well into the 2016 season, finishing second in the league in both receptions and yards trailing teammate Adarius Bowman in both instances. Shortly after the end of their season, the Eskimos released Walker to allow him to pursue an NFL career. Walker's CFL contract was originally scheduled to expire in February 2017.
On January 5, 2017, Walker signed a reserve/future contract with the Tampa Bay Buccaneers, reuniting him with college teammate Mike Evans. He was released by the Buccaneers on September 2, 2017 after recording just one reception for 15 yards in the preseason.
Edmonton Eskimos (second stint)
On September 6, 2017, it was announced that Walker had re-signed with the Edmonton Eskimos. Walker only played in eight games for the Eskimos in 2017, but caught 48 passes for 634 yards with two touchdowns. On January 12, 2018, the Eskimos announced that they had signed Walker to a one-year contract extension through the 2018 season. Walker was fourth in the league in receiving yards in early September 2018 when it was announced we would miss the next six to eight games with a knee injury. Walker missed the rest of the season, but was still named a divisional All-Star.
Toronto Argonauts
As a highly coveted free agent, Walker visited with Toronto Argonauts General ManagerJim Popp over several days, and eventually signed a one-year contract reportedly for $275,000 Canadian, making him the highest paid non-quarterback in the CFL. Walker's 2019 started off slowly, seeing few targets from starting quarterback and fellow former Edmonton player James Franklin, who resorted to check downs to Llevi Noel. However, once Franklin was injured and McLeod Bethel-Thompson was inserted for the majority of the year, Walker's playmaking abilities as a deep threat could be fully utilized. His two best games had 9 catches and two touchdowns each, and yardage totals of 188 and 203 yards. Walker finished the last few games of 2019 on the injured list, but had made 65 catches for 1,040 yards and 6 scores. He was the team leader in receiving yards by 1 yard, and was named the Argos nominee for Most Outstanding Player award. Both Walker and Green were named divisional All-Stars, the only Toronto players from the offense to be named to the list. Walker was not re-signed by the Argonauts following the 2019 season and became a free agent on February 11, 2020.
