The club have secured the former Central Coast Mariners striker's services just days after the Jets picked up their second wooden spoon in three seasons and promptly sacked coach Mark Jones.
O'Donovan had been heavily linked to the Jets in recent weeks, a rumour further fuelled over the weekend when Mariners coach Paul Okon reluctantly confirmed his 31-year-old top-scorer was on the way out.
It's believed the Jets offered him over and above anything the cash-strapped Mariners could put on the table, while also reportedly beating competition from Western Sydney Wanderers and Brisbane Roar.
"This wasn't the situation that I set out to achieve at the start of the season but this is the industry of professional sport," O'Donovan said on Wednesday.
"I've got a young family and this is an opportunity that I couldn't pass up.
"I can't thank everyone involved with the Mariners enough, I do not have a bad word to say about the Central Coast Mariners.
"I've loved my time here. It's a shame we couldn't have experienced more success but I wish the club every success moving forward, and I mean that from the bottom of my heart."
O'Donovan has netted 11 goals this campaign for a struggling side and is a coup for a Jets outfit that scored only once in their final six games.
Jones' team conceded a record 19 unanswered goals in that period to suffer an unceremonious fall from finals contenders to wooden spooners.
Talks with other potential recruits have been put on hold until a new coach is in place.
Jets chief executive Lawrie McKinna is hopeful of appointing someone before the squad breaks for holidays on May 5 and said the club will favour candidates with experience.
O'Donovan will join his new teammates for the start of pre-season training in late June, and could make his club debut on July 8 when the Jets host Chilean Primera Division side Audax Italiano at McDonald Jones Stadium.
Meanwhile, Adelaide have confirmed the A-League's worst-kept secret that first-choice Mariners goalkeeper Paul Izzo is returning to the Reds on a three-year deal.
The 22-year-old started his professional career with Adelaide as back-up to captain Eugene Galekovic, who is rumoured to be joining Melbourne City after a decade with United.