Lemaire, who will report to Steve Troote, regional senior vice-president of Northern Europe, joins from RB's US division, where he was marketing director for Air Wick.
At the same time, Adam Rodgers has joined the UK business as sales director. Rodgers has also arrived from RB in the US, where he was the customer category director. He replaces Kerry Miller, who has moved to a position with RB in Australia.
Gaa had held the role of marketing director for RB UK since July 2010. He previously oversaw the company's health marketing unit.