The ex-TBWA board account director will initially have no formal title.
But Lace said: "Russell will be my confidante, my adviser and my Mr Fixit."
Hopson, who becomes Lace's first signing since moving to Grey at the beginning of the month, is expected to have an influence on the agency's relaunch which is planned for the end of February.
The relaunch is expected to involve a management restructure and further senior appointments, including a replacement for Tim Mellors who is likely to quit as the chief creative officer next year.
Hopson, 32, a former marketing director for English Heritage, is likely to have a wide-ranging brief. His arrival at Grey renews a working relationship with Lace that began when both were at Saatchi & Saatchi in the early 90s.
Hopson was the board account director on Nissan at TBWA from 1998 to 2000 before becoming the head of marketing communications at the Science Museum.
He rejoined TBWA from English Heritage in August.