Kemsley, who will have an equity stake in the agency, takes over from Christine Jones. She has parted company with MWO after less than a year to follow its £35 mill-ion Direct Line account to Clemmow Hornby Inge.
MWO's future was called into question last year, after the loss of Direct Line and its £29 million AOL business to Grey London. However, Tim Mortimer, MWO's managing partner, said two yet-to-be-announced account wins totalling £17 million would safeguard its future.
He added: "We believe in single-minded mass-market campaigns and that's what Adrian does best."
Kemsely said: "I'm doing this because it feels right."