Otto Sonnleitner was born on November 20, 1906, in Würzburg, Germany. His father, Ludwig Sonnleitner, a sculptor, moved from Landau an der Isar to Würzburg around 1900. Before the outbreak of World War I, Ludwig established his own workshop.
Upon finishing his studies at the Oberrealschule in Würzburg, Sonnleitner attended the Polytechnic in his hometown, where he learned to draw. In 1925, after completing his apprenticeship, he moved to Munich. There, he was mentored by Valentin Kraus, the future head of the monastic sculpture workshops of Münsterschwarzach.
In Munich, Sonnleitner undertook small, low-paying jobs, including creating inscriptions for the war memorial in Hofgarten. He began his studies at the Academy of Fine Arts, initially under Karl Killer, then Fritz Behn. He studied with Behn until 1931 before becoming a master student of the sculptor Josef Wackerle. By 1937, he had completed his studies and established his own workshop in Munich the following year.
Sonnleitner started receiving commissions from Würzburg in 1935, including a relief for the University Women's Hospital. Later, he crafted a piece for the Goethe School in Würzburg and showcased his works at five Great German Art Exhibitions in Munich between 1937 and 1944.
In 1947, following his father's death, Sonnleitner returned to his hometown and took over his father's workshop. He received additional commissions in and around Würzburg. One of his final works was the bust of Jean Paul for Walhalla, created in 1973.