Following a prolific school career, including an innings of 400 not out as a 15-year-old, he made his entry into the first-class cricket and scored a triple-century in his second match. This innings of 314 not out helped set a series of firsts for Mumbai. It was the first occasion that a batsman had made a triple century for Mumbai away from home and, in putting on 459 runs with his opening partner Sulakshan Kulkarni, the pair became the first from Mumbai to pass 400. The Indian Express wrote, "Such was his temperament during the 675 minute stay that it was hard to believe he was playing only his second match. What was more praiseworthy was the youngster's ability to find gaps at will."

Jaffer represented Scholes CC in the Huddersfield Drakes League for a number of seasons as their overseas player. For the 2010 season he moved a few miles down the road to Skelmanthorpe Cricket Club, and broke the league record for runs scored in a single season. In the 2011 season Jaffer signed to Himley CC in the Birmingham and District Premier League.In his Test career so far, Jaffer has five centuries of which two were double-centuries. He has Test centuries against Pakistan, England, West Indies and South Africa.

As of the 2013 season Wasim Jaffer travelled to England where he played for Ainsdale CC in the LDCC league. Here he enjoyed a successful first half of the season scoring multiple centuries and a had a strike rate of 97.93 and a top score of 153 not out. Injury curtailed his time at Ainsdale as he had to return home to India for an operation on his knee. In June 2015, Jaffer switched to Vidarbha from 2015/16 Ranji season.On 1 January 2018, Vidarbha won Ranji Trophy and in the final against Delhi, Jaffer hit the winning boundary.

In November 2018, in the third round of the 2018–19 Ranji Trophy against Baroda, Jaffar became the first batsman to score 11,000 runs in the Ranji Trophy. The following month, in round seven of the tournament, he scored his 55th century in first-class cricket. Later the same month, he equalled the record for playing in the most matches in the Ranji Trophy, with 145. He was the leading run-scorer for Vidarbha in the group-stage of the 2018–19 Ranji Trophy, with 763 runs in eight matches. In the quarter-final match of the tournament, against Uttarakhand, he scored his 19,000th run in first-class cricket. In the opening round of the 2019–20 Ranji Trophy, Jaffer became the first cricketer to play in 150 matches in the Ranji Trophy. On 7 March 2020, Jaffer retired from all formats of the game.