Both agencies are part of the Interpublic Group of Cos.
Mr. Kelly, 52, left Lowe in February.
He will be responsible for business development, account management and client relationships, according to Martin Agency CEO John Adams.
"He's a guy you don't let go by if he's available," said Mr. Adams, who is expected to announce another management change this week. "He's just a guy that's one of the real first-rate senior-level people in the business."