The Curacao international has signed a two-year deal at St Mary's after boss Ronald Koeman revealed on Monday that a move for the 25-year-old was close.
With left-back Ryan Bertrand having undergone knee surgery, Martina will now link up with his new team-mates for a pre-season tour of Austria knowing there is a chance to establish himself in Koeman's side before the new Premier League season kicks off.
Martina's versatility also appears to have convinced Koeman to once again return to the Eredivisie to strengthen his ranks.
"Ryan had a small surgery in both his knees 10 days ago and will be out for the coming weeks," he said on Monday.
"The number of defenders we have in the squad is too small, so we need more competition
That player is available for three of the four positions in defence, and so would give us more players for a tough season."
Talking after the deal was confirmed, Martina said there were many factors that made a move to Southampton, who will play in this season's Europa League, attractive.
"I'm very happy to be here at a big club like Southampton," he said
"I've followed Southampton now for two years and I see they are now a big club
I know Ronald Koeman and Erwin Koeman - I worked with Erwin for one year and everything was good
He knows my qualities and I know what he wants
"It was a dream for me to play in the Premier League and finally I can play now
I hope to play many games and show the fans who I am."
He is the fourth player to move to St Mary's this summer, joining the acquisitions of Juanmi and Cedric Soares and the loan signing of Fulham goalkeeper Maarten Stekelenberg.
Whether fellow defender Toby Alderweireld will further add to Koeman's defensive options continues to be unclear as the Belgium international, who impressed on loan at Saints last season, has reportedly undergone a medical at Tottenham - despite the potential threat of legal action from Southampton who claim they had a deal in place to sign the player from Atletico Madrid.
Source : PA