Mudassar made his debut in Test cricket for Pakistan against Australia in Adelaide on 24 December 1976. The son of Test cricketer Nazar Mohammad, he followed in his father's footsteps to open Pakistan's opening batting. Mudassar now resides in Bolton, England. He played for many prominent league teams in Pakistan, and played his last Test match against New Zealand at Auckland on 28 February 1989, but he continued playing first-class cricket until 1993. He became the second Pakistani after his father to carry the bat as an opener in the fifth Test of the 1982–83 series against India.

One time, Mudassar held a record for highest partnership in Test Cricket of 451-runs, 3rd-wicket with Javed Miandad against India at Hyderabad, Pakistan in 1982–83. He also holds the record for the slowest Test match century and also in terms of minutes (557). He was also a useful bowling option for his captain and earned the reputation of a shock bowler because he was good at breaking long partnerships and batsmen who played long innings.

In the mid-1980s, Mudassar became a spokesman for the Pakistan players' association and claims that criticisms he made about the Pakistan Cricket Board (PCB) led to him being omitted from the Pakistan side.

After retiring from professional cricket, Mudassar became national coach for Pakistan and has coached a number of other teams, including Kenya's national team in the season of 2005. In 1982 he earned the title of 'Golden Arm' at Lord's for his match winning bowling spell against England.

Test centuries