The girl group will flick the switch and perform their new single, My Heart Takes Over, at the Marks & Spencer store at Marble Arch next Tuesday.
They will follow in the footsteps of Westlife, Leona Lewis, the Sugababes and the Spice Girls, who have all lit up the mile-long lights in the past.
The free Oxford Street lights celebration, which start at 5pm, comes as The Saturdays prepare to release new album On Your Radar on November 21.
In December they will set out on the road for an arena tour that calls at Bournemouth, Liverpool, Cardiff, Brighton, Birmingham, Manchester, Newcastle, Nottingham, Glasgow, Sheffield, London, Belfast and Dublin.
Jace Tyrrell of the New West End Company, which represents retailers in Bond Street, Oxford Street and Regent Street, said: "London's iconic Oxford Street lights will capture the imagination of the tens of millions of visitors over the Christmas period to the West End.
"With retailers all lit up for the festive season, the West End will attract visitors looking to start their Christmas shopping."