Fessler was born Majella Nicola Fessler in Milwaukee, Wisconsin, the granddaughter of the prominent architect Erhard Brielmaier. She joined the Sisters of St. Francis when she was seventeen years of age and went on to graduate from University of Wisconsin–Milwaukee, and the School of the Art Institute of Chicago.
One of the most publicly known artists within the Brielmaier artist family, she was profiled by Life Magazine in a 1953 feature story written by Jaqueline Mitchard. Prior to the publication, Fessler was being asked by the Church to reconsider whether she should she remain in the convent due to what the church hierarchy was 'seeing' in her artwork. Fessler's reply was that if there was a sexual nature they were 'seeing' in her artwork, they should look within themselves for the answer to what 'they' were 'seeing'. Fessler went on to found the Art Department at Cardinal Stritch University, becoming the Chair of the Art Department as well as founding the much acclaimed Studio San Damiano art gallery and studio for artists and education; based on her philosophy of, "Nature is God's art and art is man's nature" as well as the Brielmaier tradition of, "A child who learns to create will not destroy."
Fessler created over 600 paintings, most of which are now held in private collections, some within art galleries or museums such as the Haggarty Museum at Marquette University. Two of her elaborate huge sculptures made of precious woods to bring color distinction are featured on the entire walls of the Marquette University second and fourth floor library. Her hand carved 16-foot crucifix, altar sculptures or stone carvings can be seen within churches throughout the United States. Her Studio San Damiano, where she had worked for decades with artist Irene Kilmurry, closed on April 14, 2004.
Fessler's Franciscan spirit of poverty and humility prevented her from having a publicist or agent, yet still went on to be listed in Who's Who of American Artists, Who's Who of Women, and named as one of the 100 Most Distinguished Women of Wisconsin. She was the first women inducted into the Wisconsin Architects' Association.
- Patricia Lefevere, Nun teaches that `we are all born artists' – Franciscan Sr. Thomasita Fessler – Interview, National Catholic Reporter, Oct 22, 1999.
- JS Online: Fessler dedicated her life to God, art