Originally signed on loan from Sheffield Wednesday, the Owls having signed Mark from SPL side Motherwell in January 2011 for an undisclosed fee.
Equally at home at the centre of defence or at left back. Reynolds was a product of the Motherwell youth academy who graduated to senior football during the 2005-06 campaign. He went on to become a mainstay in the Motherwell defence, making a total of 192 appearances. The versatile defender has also represented Scotland at Under-19, 20 and 21 level.
After two loan spells at Pittodrie, Mark was eventually signed on a four year contract, making him a key figure in the Club's long term plans. His consistency in his defensive role and strong influence around the dressing-room saw him appointed vice-captain of the team and during the extended absence through injury of captain Russell Anderson, Mark wore the captain's armband with aplomb.
On 31st January 2019 Mark agreed to join Dundee United for the remainder of the 2018-19 season and signed a pre-contract agreement with them on 4th April 2019.
The contribution that Reynolds made to Aberdeen's recovery under the management of, particularly, Derek McInnes, cannot be overstated and he will always be held in high regard by everyone associated with the Dons.