Anglesea Road, St Michael’s Road and Park Road were closed to motorists and a number of spectators gathered near Victoria Baths to watch the 450-ton structure swing into place.
A temporary bridge had served train services going to the Harbour station since December 1972.
But on this day the trains stopped at Portsmouth & Southsea station and passengers finished their journeys on buses.
Made of girders, with a concrete and composite steel deck, the bridge was lifted into position by two 10-ton winches.
The bridge is still in place today.