Appearing at the High Court in Glasgow, Michael Handley, 39, of Dumfries, admitted hiding criminal gains through his firm Lochthorn Car Sales in the town's Locharbriggs.
The offence was committed between May 2003 and December 2006. Hanley, sole proprietor of the company, is currently serving six years for assault to injury and danger of life.
Judge Lord Turnbull deferred sentence until next month. Handley faces a further hearing under the Proceeds of Crime Act in April.