The duo replaces Sally Ann Triplett and Niamh Perry as mother and daughter Donna and Sophie Sheridan respectively.
Hateley, who played the role of Donna before Triplett, is a West End regular whose credits include Chicago, Mary Poppins, Les Misérables and Joseph And The Amazing Technicolor Dreamcoat.
Mamma Mia!, which has now extended its booking period to February 2011, weaves the songs of 70s Swedish pop group ABBA into a Greek island-set story by writer Catherine Johnson about a girl searching for her father on the eve of her wedding day. The combination of sea, sequins and sing-along songs has proved irresistible to audiences on screen and stage; the original West End show has been running for more than 10 years and has spawned countless international productions, while a movie version proved a summer hit in 2008.
Hateley and May join a cast which also currently includes Katy Secombe, Jane Gurnett, Norman Bowman, Paul Ryan and Christopher Hollis.