Pompey have paid an undisclosed fee to bring Michael Smith back to Fratton Park.
The 24-year-old scored four times in 16 appearances while on loan from Swindon during the second half of last season.
Now Paul Cook has moved to make the striker’s stay a permanent one, recruiting him on a two-year deal.
Smith represents Pompey’s fifth signing of the summer following the arrivals of Matt Clarke, Danny Rose, Carl Baker and Drew Talbot.
He scored 26 times in 72 matches while with the Robins, including 18 goals during the 2014-15 League One campaign.
The former Charlton player has also spent time on loan at Accrington, Newport County, Colchester, AFC Wimbledon and Barnsley.