Manx advocate John Quinn has been appointed by The Queen for a period of 12 months.
Mr Quinn said: "I will endeavour to serve the crown and the Isle of Man to the best of my abilities."
Mr Harding, 50, who has held the position since November 2010, was suspended on 3 October after appearing in court to face criminal charges.
He is currently on bail facing six charges - including three counts of forgery.
A government spokesman said Mr Harding, who earns in the region of Â£160,000 a year, has been suspended on full pay.
From March, Mr Quinn will serve as legal advisor to the the island's lieutenant governor, council of ministers, government and statutory boards, while Mr Harding is unable to undertake his duties.
Mr Harding has so far appeared in court twice, along with the deputy assessor of income tax, Colin Goodwin.
The Isle of Man has appointed a new law chief following the suspension of the attorney general, Stephen Harding.