Her selection follows the appointment of Delaney Lund Knox Warren & Partners to run the campaign in April.
Print and viral executions will launch in the next week in a bid to raise awareness of testicular cancer.
In the 80-second viral spot, Stevens is shown in her bedroom in just her underwear. She provocatively tells male viewers to put their hands down their trousers and to get hold of their testicles. She then goes on to explain exactly how to detect cancerous lumps and bumps.
The former S Club singer follows in the footsteps of Robbie Williams, who donned fake breasts in Everyman's 1999 TV campaign.
The Everyman campaign was set up by The Institute of Cancer Research in 1997. It aims to raise awareness of male cancers (particularly prostate and testicular) and to raise money to fund research within the UK's first dedicated male cancer research centre.