After high school, Willer graduated from the UFA junior studio under Else Bongers with musical, singing and dancing training. In 1959 he passed the stage examination. This was followed by engagements at the Bochum theater, the Zürich theater, the Lower Saxony State Theater in Hanover and the Thalia Theater in Hamburg. He made guest appearances on many other stages and at festivals and took part in numerous tours. His roles include Moritz Stiefel in Spring Awakening, Ferdinand in Kabale und Liebe, the title role in Clavigo, the title role in Don Karlos, Lancelot in The Merchant of Venice, Silvius in As You Like It, Cornelius Hackl in Hello, Dolly!, Truffaldino in The Servant of Two Masters, Sigismund in Life is a Dream, Andri in Andorra, Eisenring in Biedermann and the Arsonists and Prince in Carl Sternheim's Citizens Schippel. Willer is best known for roles in television series. For example, he played for the ARD in PS – stories about the car, for the ZDF in the Der Alte and in the WDR series Klimbim. He was the leading actor in the erotic film Help, a virgin loves me