Born in Brand, Reger studied music in Munich and Wiesbaden with Heinrich Reimann. In 1901 he settled in Munich, where he taught organ and composition, and from 1907 he worked in Leipzig, where he was music director of the university until 1908 and professor of composition at the conservatoire until his death. Among his students there were Joseph Haas and George Szell. From 1911 he conducted the court orchestra at Meiningen until it was disbanded in 1914, when he moved to Jena. He died of a heart attack.
Reger was a very prolific composer, although few of his compositions are well known today. Many of his works are fugues or in variation form, including what is probably his best known orchestral work, the Variations and Fugue on a theme of Mozart (based on the opening theme of Wolfgang Amadeus Mozart's Piano Sonata, K. 331). He also wrote a large amount of music for organ, including the Fantasy and Fugue on BACH (based on the BACH motif), and music in virtually every other genre (opera being a notable exception).
Reger saw his music as being part of the tradition of Ludwig van Beethoven and Johannes Brahms, and his work often combines the classical structures of these composers with the extended harmonies of Franz Liszt and Richard Wagner and the complex counterpoint of Johann Sebastian Bach.