Gildart was released by the Tigers late last year, with the final year of his deal after moving from England still to run.
It was unclear at the time whether Gildart would return to England or find a new home in the NRL, however, he will head to Redcliffe and link up with former England coach Wayne Bennett.
Gildart struggled to find consistent game time at the Tigers during his first year down under, and while he started the season, a mixture of injuries and form stopped him from being a permanent part of Michael Maguire, and then Brett Kimmorley's side.
He was loaned late in the season to the Sydney Roosters and played a handful of games for the tri-colours.
A former English representative, Gildart had played 129 games for Wigan before making the switch to the NRL.
Dolphins CEO Terry Reader said Gildart was a quality addition.
“Oliver has played rugby league at Test level and is a player who is fast, elusive and has great footwork,” Reader said.
"Wayne Bennett coached him on a Great Britain tour so knows him well, and we believe he may only have just scratched the surface of what he can do in the NRL."
“Importantly, his signature adds another strong option to our backline list.”