The former "Beverly Hills, 90210" heartthrob also is to direct an episode of the second season of the series.
Production on the 13 episodes for Season 2 is to begin in Nova Scotia April 1, with an eye towards a summer premiere.
Syfy said Priestley's "Haven" character, Chris Weekly, will be a "handsome but anti-social marine biologist who must deal with an affliction most would consider a blessing."
The series follows an FBI agent who takes up residence in Haven, Maine, and soon discovers the small town is a refuge for people with a range of supernatural powers. The show co-stars Emily Rose, Lucas Bryant and Eric Balfour.