The win sets up an October re-match with his old rival Chris Eubank in the first of a proposed series of contests aimed at unifying the super-middleweight division.
Gent, a former cruiserweight who has mixed in good company, but despite a promising opening, things began to slip away from the challenger in the third, when a right-left combination sent him over for a count of seven.
Gent was swiftly back on his feet, taking the fight to his rival, forcing Benn to back away and cover up.
In his desire to inflict damage, the Streatham man left himself open, and though Benn was forced to take cover under a barrage another two-punch combination produced a second knockdown.
That would have done for most fighters but Gent was up at eight and continued to slug away. However his resistance was visibly on the wane and a third knock-down from a left hook occurred as the round came to an end.
For all the challenger's courage the end was inevitable: Gent was down twice in the fourth, forcing referee Larry O'Connell to bring matters to a close after 35 seconds of the round.
PROFESSIONAL PROMOTION (Olympia): 12-rd WBC super-middleweight title: Nigel Benn (Ilford, holder) bt Lou Gent (Streatham) rsf 4th. 12-rd vacant Penta-Continental middleweight title: S Collins (Dublin) bt G Botes (SA) rsf 7th.Reuse content