Willi Mueller was born on 27 June 1951 in Unterkulm in the canton of Aargau. There he went to school until he attended the teacher's seminar in Aarau. After three years of school service in the country he moved to Zurich and attended the School of Arts and Crafts, today's College of Design. Willi Mueller stayed from 1974 to 1978 and graduated with a diploma as a drawing teacher. His teachers were mainly R. Frauenfelder and Theo Kneubuehler.

After this time he started a part-time drawing course at a grammar school in Zurich, interrupted by a one-year teaching position for painting at the School of Design in Zurich. Early on, however, he also began to work independently as an artist. In 1981 he moved his residence and studio to Lake Biel in Nidau. His wife Dorette comes from this area. Together they have three children. Willi Mueller was already a Visarte member in the canton of Aargau and took part in activities such as the exhibition Dialogoge at the Kunsthaus Aarau in 1989, where he researched the painter René Auberjonois. The canton of Aargau also supported his work in that year with a scholarship. Later he moved to the Visarte section in Biel, where he is also well established in the art scene.

After he had experimented extensively with multimedia techniques during his studies in Zurich, he soon decided to focus on painting, in his own studio. For a few years he met with young Bernese painters informally in the group "Entstand".
Willi Mueller has the feeling that he took a long time to develop a mature, independent style of painting. Through internal upheavals, construction and collapse, he searches for a formula where the secrets of the people, the things and the places of this world can be experienced through art.