2005 was Biffle's breakout season. He won six races (at California Speedway, Texas, Darlington, Dover, and Michigan along with the season finale at Homestead), the most of any driver that year, and qualified for the Chase for the first time in his career, bringing home a second-place finish in the standings, 35 points behind champion Tony Stewart; Biffle tied with his teammate Carl Edwards in points but won the tie-breaker based on race wins.