Hart had signed a pre-contract agreement to return to Aberdeen in the summer, having left Pittodrie 18 months ago.

But the Dons were keen not to wait until his current deal with Livi expired and it appears that a transfer fee of around �30,000 has been agreed between the clubs.

Aberdeen manager Steve Paterson admitted he had unsuccessfully tried to sign Hart for Inverness Caley Thistle and was delighted to have finally got his man.

I think it's an exciting time as Steve Paterson and Duncan Shearer have brought new life to the club Michael Hart

"I've been an admirer of Michael's ever since his early days at Aberdeen," Paterson told Aberdeen's official website.

"I've had to wait a long time, but I'm convinced it will be well worth the wait as he's a versatile player who is comfortable in a number of positions.

"I'm happy we now have a nucleus of talented Scottish defenders at the club who can take us forward."

Hart said he was looking forward to working with the Dons' new managerial partnership of Paterson and Duncan Shearer.

"I like the way they think about the game so the outlook for the Dons is a positive one," he told the Aberdeen website.

Hart is ineligible for Saturday's Scottish Cup tie against Queen of the South, having missed the signing deadline.

His move ends a controversial period during which Livingston chairman Dominic Keane complained that the Dons had broken a gentleman's agreement between SPL clubs not to approach each other's players while still under contract.

Livi rejected Aberdeen's opening bid to sign Hart during the January transfer window.

Meanwhile, Livi hope to conclude the signing of 35-year-old former Barcelona midfielder Guillermo Amor on Monday after negotiations went well on Friday.