Keeley, who was set to join the Storm next season on a two-year deal, has beaten the June 30 cut-off and will be available for Melbourne's home clash with Gold Coast on July 12.
The Storm's depth has been seriously tested by a spate of injuries and unforeseen events.
Star back-rower Eliesa Katoa is out of action for the season after a medical episode following a head knock at last year's Pacific Championships.
Prop Tui Kamikamica is on the road to recovery after suffering a stroke while in-form second-rower Ativalu Lisati sustained a syndesmosis injury in the 30-4 loss to Manly on Saturday night.
Centre Jack Howarth, who can play second-row, is on the injured list with a quad complaint. Second-rower Joe Chan, who played centre against the Sea Eagles, was replaced after suffering back spasms.
Keeley's arrival couldn't come at a better time as the Storm, on 16 points, still hold hope of making the finals after winning five of their past seven matches.
Keeley, 23, came through the Newcastle system and he debuted before joining the Dolphins where he has played 28 of his 30 NRL games since 2024.
The Storm have a bye in round 18 but club director of football Frank Ponissi said he would be in the frame for the clash with the Titans.
"He's a quality young player and having him arrive earlier than expected is a great outcome for both the club and Oryn," Ponissi said.
The Dolphins will miss Keeley who has done a solid job during his tenure and particularly throughout the current the State of Origin period.
His absence for Sunday's away clash with Newcastle will test the third-placed Dolphins who have five players involved in Origin and co-captain Isaiya Katoa out of action with a broken wrist.
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