=== Ultimate Fighting Championship ===
Den [[4. maj]], 2017, offentliggjorde Gaethje at han havde skrevet kontrakt med [[Ultimate Fighting Championship]].<ref>{{cite web|url=http://www.sherdog.com/news/news/Justin-Gaethje-Says-UFC-Contract-Signed-Wants-Scariest-Lightweight-Possible-121065|title=Justin Gaethje Says UFC Contract Signed, Wants ‘Scariest Lightweight Possible’|publisher=sherdog.com|date=4. maj 2017}}</ref> Det blev offentliggjort den 14. maj at han ville debutere mod [[Michael Johnson (kæmper)|Michael Johnson]] den [[7. juli]], på ''[[The Ultimate Fighter: Redemption Finale]]''.<ref>{{cite web |url=https://www.mmamania.com/2017/5/12/15633866/michael-johnson-vs-justin-gaethje-set-to-headline-tuf-25-finale-on-july-7-in-las-vegas|title=Michael Johnson vs. Justin Gaethje set to headline TUF 25 Finale on July 7 in Las Vegas|publisher=mmamania.com|author=Dan Hiergesell|date=2017-05-12|access-date=2017-05-12}}</ref> Gaethje vandt en lige kamp via TKO i 2. omgang ved en kombination af slag og knæ.<ref>{{Cite news|url=http://mmajunkie.com/2017/07/tuf-25-finale-results-justin-gaethje-tko-michael-johnson-memorable-ufc-debut|title=TUF 25 Finale results: Justin Gaethje TKOs Michael Johnson in memorable UFC debut|date=2017-07-08|work=MMAjunkie|access-date=2017-07-08|language=en-US}}</ref> Sejren indbragte Gaethje Fight of the Night og Performance of the Night bonus-prisen.<ref name="autogeneret1">{{Cite news|url=http://mmajunkie.com/2017/07/tuf-25-finale-bonuses-justin-gaethje-debut-double-bonus-100000-michael-johnson-tecia-torres-ufc|title=TUF 25 Finale bonuses: Justin Gaethje's sick, sick debut was a double winner for $100,000|date=2017-07-08|work=MMAjunkie|access-date=2017-07-08|language=en-US}}</ref> [[Sherdog]] kårede denne kamp som den bedste kamp i 017,<ref name="FOTY"/> og 2. omgang som årets bedste omgang.<ref name="ROTY"/>
Levende_personer Sport