Stefan Denifl (born 22 September 1987) is an Austrian former professional cyclist, who rode professionally between 2006 and 2018 for seven different professional teams. In 2019, Denifl confessed to doping during a five-year period in his career, and was given a four-year ban from the sport; as a consequence of this, Denifl received a two-year sentence in 2021 for serious commercial fraud.

Born in Fulpmes, Denifl began racing in 2001 with "Team Bike Denifl" as a mountain biker. In 2003, he moved to the road, riding for "Team ÖAMTC Recheis Lattella". From 2004, he focused on road cycling. In 2005, he was signed by Heiko Salzwedel for the T-Mobile Development Programme and included his first experience with the professional cyclists. In 2006, he signed with his first UCI Continental team Vorarlberger, and from 2007 to 2009 he was part of Elk Haus–Simplon. In 2009, he rode as a trainee for Cervélo TestTeam,^[2] and rode with them as a full professional the next year. In 2012, he rode for a year with Vacansoleil–DCM^[3] before joining IAM Cycling the following year.^[4] In October 2016, Aqua Blue Sport announced that Denifl, alongside IAM team-mate Leigh Howard, would be part of their inaugural squad for the 2017 season.^[5] After Aqua Blue disbanded in the later summer of 2018, in October of that year Denifl was initially announced as a member of the CCC Team for the following season. However, in December 2018 the team announced that they and Denifl had mutually agreed to cancel his contract due to personal reasons, which were not specified at the time.^[6]