The 142-ball effort, studded with 18 fours and six, by the East skipper and erstwhile India captain helped his side take a sizeable 113-run first innings lead over North who were placed at 106 for three in their second innings at stumps.
East owed their edge to Ganguly who had taken three crucial wickets in North's first innings, restricting them to 178.
The all-round effort of the Bengal batsman, especially his fluent strokemaking, laid to rest the intense speculation over the last few days over his form and fitness, the two factors which saw him losing his place and captaincy of the Indian team.
Ganguly came in when his side was in real trouble at 54 for three but showed good temperament in steadying the innings with a mix of aggression and patience.
Resuming this morning at 77 for four, Ganguly stitched two useful partnerships with his Bengal teammates Laxmi Ratan Shukla (31) and Deep Dasgupta (57).
He added 125 runs with Shukla (5x4) for the fifth wicket before putting on 72 runs for the sixth with Dasgupta who slammed 11 fours.
Ganguly, who was batting on 19 overnight, reached his hundred before lunch as East Zone scored 158 runs in the morning session in just 30 overs.
However, Ganguly was dismissed just after lunch off leg spinner Amit Mishra, the thick outside edge being taken by Pankaj Dharmani.