The Make Mine Milk promotion also features the cast of The A-Team, Liam Neeson, Bradley Cooper, Quinton Jackson and Sharlto Copley.
Posters of the stars posing with milk moustaches will appear on billboards and buses across the UK.
Celebrity chef Gordon Ramsay and singer Pixie Lott have already appeared in the adverts.
According to WENN, Usher said: "Milk is music food for sure. It keeps me fresh when I'm recording and helps give me the energy to perform night after night when I'm on tour."