[4][5] He started his career with Mohun Bagan.He appeared on Calcutta Football League with club East Bengal from 1984 to 1991 and again from 1992 to 1994, and captained the team in 1989–90.

[9][10][11][12] Krishanu began his professional career in the Calcutta Football League with Police A.C. in 1979,[13] and groomed under Achyut Banerjee.

[17] He was part of the team that won Federation Cup in 1985 and appeared in qualifiers of 1985–86 Asian Club Championship in Saudi Arabia.

He later joined his employer side – Food Corporation of India FC in 1995, which was also CFL outfit, having players like Narinder Thapa, Aloke Mukherjee.

He was one of the highest paid Indian footballers of the eighties and along with his close friend and fellow midfielder Bikash Panji with whom he formed a lethal combination on the field.

[31] Krishanu made his senior international debut for India on 22 June 1984 in the Great Wall Cup against China.

Krishanu represented India in 30 list 'A' matches and scored 9 goals,[2] including a hat-trick at the Merdeka Tournament against Thailand in Malaysia, 1986.

[32] Selected international goals: 1986 After his retirement in 1997, Dey went on to choose a managerial career and coached Food Corporation of India FC.