The How We Do singer has apparently signed a £500,000 deal and already shot campaign photos for the label, run by Madonna and her daughter Lourdes, according to The Sun.
It was reportedly Lourdes who championed Rita, 22, as being the perfect fit for their brand.
A source told The Sun: 'Lourdes has been a fan of Rita for a while and has been to many of her gigs. She persuaded her mum to see her.'
'They met at the Met Ball in New York last week and Madonna admired Rita's attitude so signed the idea off.'
'Rita jumped at the chance because she's such a fan of the Queen Of Pop. She also hopes it will help her crack the States in the same way she has the UK.'
Kelly Osbourne, Georgia May Jagger and Taylor Momsen have all modelled for Material Girl in the past.
From Press Association Via Yahoo! News