The Hills star, 22, will appear in Into the Blue 2, the follow-up to Alba's 2005 beach flick.
Patridge plays a no-nonsense, beautiful beach babe whose boyfriend caters to her every command, according to the Hollywood Reporter.
The role is "giving me the chance to show people [what I can do]," Patridge, who recently canned her agent for not getting her enough gigs, told Ryan Seacrest on May 8. "This is why I moved to L.A."
Could another Hills feud start? Patridge is the first star from the reality show to begin acting in movies. (Pal Lauren Conrad appeared in 2007's Epic Movie as herself.)
"The drama is still unfolding," Patridge told Seacrest.
The Hills' season finale airs tonight. Usmagazine.com first reported that the MTV hit was renewed for a fourth season.