Tillman began his career as a football executive in 1981 as a member of the Houston Oilers' public relations department. The following year, he received his first job in the CFL when he became the player personnel director of the Montreal Concordes. From 1984 to 1993, Tillman served as Executive Director of the Senior Bowl, a game sponsored by National Football League designed to showcase top players graduating from United States colleges.
From 1993 to 1995, Tillman was the General Manager of the BC Lions. Tillman took over a team that went 3–15 in 1992. Under Tillman, the Lions posted a 31–22–1 record and upset the Baltimore Stallions in the 82nd Grey Cup. The Lions success came in spite of regular fighting between head coach Dave Ritchie and owner Bill Comrie and a lack of team harmony.
In 1995, Norton Herrick, an Orlando, Florida real estate developer, announced plans to move the CFL's Las Vegas Posse to Tillman's hometown of Jackson, Mississippi. Tillman was to be the club's general manager, however plans fell through and the relocation did not take place and Tillman remained with BC.
In November 1995, the World League of American Football named Tillman its Director of Football Operations. Tillman, however preferred overseeing a single team so in 1997 he returned to the CFL as general manager of the Toronto Argonauts. That year, the Argonauts won the Grey Cup. However, Tillman and head coach Don Matthews had a tumultuous relationship. On March 1, 1998, Tillman officially departed the Argonauts. He then joined TSN as a football analyst. In 1999, Matthews left the Argonauts to become head coach of the Edmonton Eskimos and, after Wally Buono turned down an offer to become head coach and general manager, the Argos asked Tillman to return as GM. When the team was purchased by New York businessman Sherwood Schwarz after the 1999 season, Tillman was fired and replaced by Schwarz's cousin, J. I. Albrecht. After his dismissal, Tillman returned to TSN.
On October 23, 2001, Tillman was named the first General Manager of the expansion Ottawa Renegades. Ottawa won four games their inaugural season and seven games the following year. In 2004, the Renegades gave head coach Joe Paopao the title of director of football operations. Although Tillman was still technically general manager, Paopao was effectively general manager.
After leaving Ottawa, Tillman served as an analyst for the CBC and Rogers Sportsnet.
Part way through the 2006 CFL season, Tillman was hired as the Roughriders general manager after they fired long time GM Roy Shivers. He took over a team that had a tarnished reputation in the community after several players had run-ins with the law, including former linebacker Trevis Smith, who had been charged with two counts of aggravated sexual assault after he knowingly exposed two women to HIV without telling them. Tillman promised to clean up the team's image and the Roughriders adopted a code of conduct which required players to obey the law, act with honesty and integrity, respect others, and take responsibility for their actions.
During Tillman's three years with the team they hosted three consecutive home playoff games and played in two Grey Cups. In 2007, the Roughriders won their third ever Grey Cup. Among the key signings made by Tillman were head coach Kent Austin, defensive end Stevie Baggs, receivers Weston Dressler and Rob Bagg, defensive back Omarr Morgan, and running back Corey Holmes. He also acquired many key players who would be part of the Roughriders 2013 championship season, including Darian Durant, Chris Getzlaf, and John Chick. In July 2008, Tillman was given a contract extension through 2010.
On August 6, 2008, Tillman was sent home from a team board meeting because he was acting strangely. After he arrived home, Tillman put his hands on the hips of his children's sixteen-year-old babysitter and pulled her rear end into his body in a sexual nature. Tillman's attorney would state that Tillman was not thinking clearly because he had taken a double dose of sleep aids and pain medication for a sore back and that he did not remember what happened. On January 27, 2009, Tillman was charged with summary sexual assault. He was placed on paid administrative leave by the Roughriders on February 2, 2009.
Tillman pleaded guilty to the charge on January 4, 2010, the day his trial on this summary offence was to begin. He was granted an absolute discharge the following day and subsequently received no criminal record but was fined $50.00. Judge Murray Hinds stated that Tillman was "genuinely remorseful [and] in this case there's no suggestion that Mr. Tillman is not generally of good character. He has no prior criminal record. His behaviour towards [the teenage girl] on Aug. 6 appears to be an aberration fuelled by his consumption of two non-prescription drugs." On January 8, 2010, he resigned from his position as the Roughriders' general manager.
On September 14, 2010, Tillman was hired as General Manager of the Edmonton Eskimos. He took over an Eskimos team that had a league-worst 2-8 record. Tillman stated that his primary goal would be improving the team's Canadian players. According to Eskimos president Rick LeLacheur, the team received a "substantial" number of phone calls from fans opposed to hiring Tillman, however, the Eskimos organization had deemed him worthy of a second chance. After Tillman's hiring, the Eskimos won five out of its eight remaining games and finished out of the playoffs by only two points.
In Tillman's first full season with the team, the Eskimos finished with an 11–7 record, which tied them with the Calgary Stampeders and BC Lions for first place in the West. Edmonton defeated Calgary 33–19 in the West Semifinal, but lost to BC 40–23 in the West Final.
On December 12, 2011, Tillman traded quarterback Ricky Ray to the Toronto Argonauts for quarterback Steven Jyles, kicker Grant Shaw, and a first-round pick. The move would be criticized as Jyles struggled at quarterback for the Eskimos while Ray led the Argonauts to victory in the 100th Grey Cup.
In 2012, the Eskimos finished fourth in West, with a 7–11 record. The team struggled offensively throughout the season and started three quarterbacks Jyles, Kerry Joseph, and Matt Nichols. Edmonton lost its final three games, but was able to make the playoffs due to the crossover rule. On November 3, 2012, eight days before the Eskimos playoff game against the Toronto Argonauts, Eskimos president Len Rhodes announced that Tillman had been fired. Rhodes stated that there "no specific reason" as to why Tillman was fired, but he did point to Tillman's lack of presence in the community as an issue.
Two months after his dismissal, the Hamilton Tiger-Cats hired Tillman as a consultant. His position was described by head coach/general manager Kent Austin as being a "sounding board" for Austin. In 2014 Tillman was given the title of director of U.S. scouting and U.S. pro personnel. In 2016, he was promoted to general manager, with Austin remaining as vice-president of football operations and head coach.