Lactobacillus brevis strain 100D8 was isolated from rye silage and showed rapid acidification ability in vitro and antifungal activity against mycotoxin-producing fungi. We report here the complete genome sequence of L. brevis strain 100D8, which has a circular chromosome (2,351,988 bp, 2,304 coding sequences [CDSs]) and three plasmids (45,061 bp, 57 CDSs; 40,740 bp, 40 CDSs; and 39,943 bp, 57 CDSs).