He studied theology in Regensburg and at the University of Munich. In 1832 he received his ordination and for a period of time taught classes at the Latin School in Regensburg. Afterwards he returned to Munich and continued his studies under theologian Johann Adam Möhler (1796-1838), who was a profound influence on Reithmayr's career. After Möhler's death in 1838, he edited and published his mentor's Patrologie, oder christliche Literärgeschicht (Patrology, or Christian Literary History).
In 1836 he earned his doctorate in theology, and in 1841 was appointed full professor of New Testament exegesis at the Catholic Theological Faculty of the University of Munich, a position he maintained until his death. In 1869 he became Herausgeber of the Bibliothek der Kirchenväter (Library of the Church Fathers). The following are some of his better known writings: