The Norwich skipper struck twice in the first half to cancel out a close-range equaliser from Tractor Boys defender Damien Delaney, who was sent off in the 37th minute for a professional foul on Holt.
Keane's men rarely threatened an equaliser in the second half and, after Holt completed his treble in the 76th minute with another cool conversion, substitute Wes Hoolahan added a fourth two minutes later with a dinked finish.
The result marked a fourth successive npower Championship defeat for Ipswich but Norwich were more vibrant throughout as they moved back into the play-off zone.
Source: PA
Source: PA