Hayden, 28, has joined Standard Liege on a loan deal for the remainder of the season, with the transfer window in Belgium open until Wednesday.
The defensive midfielder is not in Eddie Howe’s plans and he was of interest to Luton Town and Sheffield Wednesday this summer.
However, a domestic transfer did not materialise in the recently concluded transfer window and Hayden will now ply his trade in Belgium.
Harkin is delighted to land him and believes Standard Liege have signed a quality performer who is also a leader on the pitch.
He also hailed the know-how that Hayden will bring to the side.
“Isaac is a quality player with physical impact and leadership”, Harkin told Standard Liege’s in-house media.
“He will also bring his great experience on Premier League pitches to his new team-mates and I am sure he will help us a lot this season.”
Hayden trained with Newcastle’s Under-21s this summer and he was not handed a squad number for the ongoing campaign.