Singh made his Test and One Day International debuts in early 1998. His career was initially affected by investigations into the legality of his bowling action, as well as several disciplinary incidents. However, in 2001, with leading leg spinner Anil Kumble injured, Harbhajan's career was resuscitated after Indian captain Sourav Ganguly called for his inclusion in the Border-Gavaskar Trophy team. In that series victory over Australia, Harbhajan established himself as the team's leading spinner by taking 32 wickets, becoming the first Indian bowler to take a hat trick in Test cricket. He is also an Officer in the Punjab Police and has held the rank of a Superintendent of police (India), reporting to Punjab Police HQ at Barnala.
A finger injury in mid-2003 sidelined him for much of the following year, allowing Kumble to regain his position as the first choice spinner in Tests and ODI's. Harbhajan reclaimed a regular position in the team upon his return in late 2004 but often found himself watching from the sidelines in Test matches outside the Indian subcontinent with typically only one spinner, Kumble, being used. Throughout 2006 and into early 2007, Harbhajan's accumulation of wickets fell and his bowling average increased, and he was increasingly criticised for bowling defensively with less loop. Following India's first-round elimination from the 2007 Cricket World Cup, Harbhajan was replaced by other spinners in the national squad for both formats. He regained a regular position in the team in late 2007 but became the subject of more controversy. He appeared in Total Nonstop Action Wrestling's Indian promotion, Ring Ka King. He was in the World Cup-winning team of 2011 Cricket World Cup.
He was awarded Shri, India's fourth highest civilian honour, in 2009.