Brian Thienes raced Formula Mazda from 1998 to 2006 garnering 15 wins and another 12 top-ten finishes before transitioning to Champ Car’s Formula Atlantic Series where he raced from 2006 through 2008.

Thienes returned to racing for the 2016 Lamborghini Super Trofeo North American Championship, competing in the ProAm Championship with co-driver Patrick Kujala. The pair had two wins and three podiums. Thienes moved to the LSTNA Am class the following two seasons as a solo driver finishing both seasons third in the Championship with two wins and seven podiums.

The 2021 season had Thienes making his IMSA Prototype Challenge debut with co-driver Jacob Eidson in the fourth round of the six round season. The pair had an impressive fifth-place finish at VIR in just their second start. Thienes competed for a full season of IMSA Prototype Challenge racing in 2022 with co-driver Patrick Kujala. The pair finished the season 3rd in the Championship. 

Thienes joined the IMSA VP Racing Sportscar Challenge in 2023. The new muilti-class sprint format seemed to be a perfect match for Thienes. He finished 3rd in the Championship in both 2023 and 2024 and finished first in the new IMSA VP Racing Sportscar Challenge Bronze Cup in 2024.