As a high school sophomore in 1970, Dorsett started at cornerback, as his coaches did not believe the 147-pound Dorsett was big enough to play running back, the position he played in junior high school. In 1971, a competition between Dorsett and sophomore Michael Kimbrough for the starting running back position ended after Dorsett took a screen pass 75 yards for a touchdown against Ambridge during the season opener.
Dorsett ended the year as an All-State selection after rushing for 1,034 yards and scoring 19 touchdowns, while leading the Vikings to a 9–1 season. He also remained a starting cornerback on the defensive side. In basketball Dorsett helped his team reach the WPIAL quarterfinals.
In 1972 he was again an All-state Selection, after setting a single game rushing record with 247 yards against Sharon, a single season rushing record with 1,238 yards and the career rushing record with 2,272 yards, while leading the Vikings to a 9–1 season. Dorsett was also a key player on the defensive side as one of the starting linebackers.
For all the ability he had, Dorsett could never lead his team to the WPIAL Class AA playoffs, because in those days the teams had to have an undefeated record. The team′s only loss in 1971 came against Sharon after Dorsett suffered a concussion and played less than a quarter, and the only loss in 1972 came against Butler while playing on a muddy field.
At the beginning of Dorsett's freshman year at Pitt, his son Anthony Dorsett was born September 14, 1973. Later in the 1973 season, Dorsett encountered some controversy when it was discovered that his son was born out of wedlock. With Dorsett having no intention of marrying his son's mother, it rankled many old-time steel workers who believed that when a man gets a woman pregnant, he should "do the right thing and marry the mother-to-be". According to Dorsett's rationing, his best way of raising his son would be through following his dreams of playing professional football as opposed to marrying a woman he wasn't in love with and working in a steel mill, something that ultimately paid off for Dorsett due to his Hall of Fame career as well as the steel industry collapsing in the late 1970s into the 1980s.
Three games into his sophomore season, he became Pitt's all-time leader in career rushing yards, surpassing the old record of 1,957 yards set by Marshall Goldberg, who helped Pitt to a national championship in 1937.
Against Notre Dame in his junior year, Dorsett had 303 yards rushing to break his own school single game rushing record. As a senior in 1976, he had a total of 290 yards against Notre Dame. He darted 61 yards on his first run of the season and tacked on 120 more by the end of the 31–10 Pitt win.
Dorsett was drafted by the Dallas Cowboys with the second pick of the first round of the 1977 NFL Draft. The Cowboys traded the 24th pick in the draft and three second-round choices to the Seattle Seahawks to move up to take Dorsett. Dorsett signed a five-year contract for a reported $1.1 million. It was the second largest contract signed for a rookie. Ricky Bell (running back) beat Dorsett with a contract the same year as the first round draft pick for $1.2 million. Dorsett played with the Cowboys through the 1987 season.
In Dorsett's rookie year, he rushed for 1,007 yards and 12 touchdowns and won the Rookie of the Year honors. Dorsett was announced the starter in the tenth game of the Cowboys' season, and he would stay the starter for many years. Dorsett was the first player to win the college football championship one year, then win the Super Bowl the next, when the Cowboys beat the Denver Broncos 27–10 to win Super Bowl XII. In his sophomore season, 1978, Dorsett recorded 1,325 yards and nine touchdowns. The Cowboys once again made the Super Bowl, and lost 35–31 to the Pittsburgh Steelers in Super Bowl XIII.
Dorsett's most productive season was in 1981, when he recorded 1,646 yards.
Dorsett had a career total of 12,036 yards in Dallas before being traded to the Denver Broncos in 1988 for a conditional fifth-round draft choice. Dorsett led the Broncos with 703 yards and five touchdowns that year, but injuries prior to the 1989 season led to his retirement.
Dorsett rushed for 12,739 yards and 77 touchdowns in his 12-year career. Dorsett also had 13 receiving scores and even a fumble recovery for a touchdown. On January 3, 1983, during a Monday Night Football game in Minnesota, Dorsett broke a 99-yard touchdown run against the Vikings, which is the longest run from scrimmage in NFL history. Dorsett broke the previous record of 97 yards, set by Andy Uram in 1939 and Bob Gage in 1949. Another notable fact about his record-breaking run was that the Cowboys only had 10 men on the field, as fullback Ron Springs was unaware of the play being called. Despite the feat, the Cowboys would lose the game 27–31.
Dorsett made the Pro Bowl 4 times during his career (1978, 1981–1983) and rushed for over 1,000 yards in 8 of his first 9 seasons. The only season that he didn't reach the 1,000 rushing yards milestone was the strike-shortened, 9-game season of 1982 which he led the NFC in rushing with 745 yards. He was a First-team All-Pro in 1981 and a Second-team All-Pro in 1982 and 1983.
Dorsett was elected to both the Pro Football Hall of Fame and the College Football Hall of Fame in 1994 and was enshrined in the Texas Stadium Ring of Honor the same year. In 1999, he was ranked number 53 on The Sporting News' list of the 100 Greatest Football Players. He is the first of only two players in history (along with former running back Marcus Allen) who has won the Heisman Trophy, won the Super Bowl, won the College National Championship, been enshrined in the College Hall of Fame, and been enshrined in the Pro Football Hall Of Fame.
Dorsett hosts the Tony Dorsett Celebrity Golf Classic for McGuire Memorial. This event, in its 17th year, has raised nearly $5 million in support of McGuire Memorial's mission.
In addition, Tony Dorsett has shifted his focus to helping improve the health of current and former professional athletes through promoting sleep apnea awareness across the country. He has teamed up with dental icon, David Gergen, and a company called Pro Player Health Alliance to hold free public awareness events in local communities all over the nation. After joining the cause of Pro Player Health Alliance and using his extensive amount of connections to players, he has helped get over 150 former players successfully treated for sleep apnea.
In November 2013, Dorsett announced he had signs of chronic traumatic encephalopathy (CTE), a brain disease found in many former football players, boxers, and hockey players. Specifically, Dorsett referred to memory loss as the major symptom affecting him in retirement.