Preliminary results for the year ended April 30 showed turnover had risen 6% to £277.8 million from £261.8 million the previous year, while pre-tax profit was up 17% to £31.7 million, £10 million higher than the previous year.
A series of new centre launches and a key acquisition of the Global Self Drive van fleet took Northgate to a record fleet size of 40,500 vehicles.
Northgate subsidiary Anglian Self Drive has absorbed the 570-van Global Self Drive fleet, doubling its size in key markets of Norwich and Ipswich and adding Peterborough to its network.
Despite the growth, fleet utilisation remains at 90%, the firm said.
Chairman Michael Waring said: 'We have now completed the third year of our five-year strategy for growth and we remain firmly on track.
'Despite more than doubling our fleet size in the past five years, we believe we are a long way from tapping the full potential of the expanding UK rental market.
'In addition, we are convinced that there are excellent prospects for growth in Continental Europe.'
Since April 30, 1999, the firm's fleet size has jumped from 26,600 vehicles, while the number of hire sites has gone from 30 to 61.