Wicketkeeper Buttler comes in as a replacement for Matt Prior, who announced on Monday that he would be taking an indefinite break from cricket due to injury following another poor performance in the 95-run loss in the second Test at Lord's.
Buttler's stock has risen significantly after some excellent recent performances in limited-overs cricket on the international stage.
Indeed, Buttler recorded the fastest one-day international hundred in England history against Sri Lanka in May, but captain Alastair Cook insisted that the 23-year-old was "not ready" for Test cricket in the aftermath of that display.
However, Buttler was called in as cover for Prior ahead of the first Test earlier this month, and will now have the chance to prove himself in the five-day game at Southampton.
National selector James Whitaker said: "The result of the second Investec Test at Lord's was very disappointing. One or two of our players had encouraging performances, however it is vital that the squad learns quickly and arrives in Southampton this week refreshed and ready to perform well in what will no doubt be another tough Test match.
"Congratulations to Jos Buttler who comes into the squad following some very exciting limited overs performances for England and a good record with Lancashire this season and fully deserves this opportunity.
"Matt Prior has contributed a huge amount to the England side over the years and should be proud of his record throughout his 79 Tests. He has decided to take time out of the game to work on his fitness and we will continue to follow his progress over the coming months."
Spin bowler Simon Kerrigan, domestic team-mate of Buttler, will not have the chance to add to his single Test appearance after being cut from the squad.
The third Test starts on Sunday.
England squad in full:
Alastair Cook (Essex) (Captain), Moeen Ali (Worcestershire), James Anderson (Lancashire), Gary Ballance (Yorkshire), Ian Bell (Warwickshire), Stuart Broad (Nottinghamshire), Jos Buttler (Lancashire), Chris Jordan (Sussex), Liam Plunkett (Yorkshire), Sam Robson (Middlesex), Joe Root (Yorkshire), Ben Stokes (Durham), Chris Woakes (Warwickshire).