Shortly after Shelton began running ultramarathons she won several races and soon became one of the top female ultrarunners in the United States. She often runs in lightweight minimalist running shoes.
In 2006, she traveled with Scott Jurek, Christopher McDougall, and several other ultrarunners as the sole female runner to Copper Canyon in the remote southwestern part of the state of Chihuahua in Mexico to run with the Tarahumara, for McDougall's book Born to Run. While running through a remote area during the trip she became separated from the group and was found severely dehydrated several hours later by a search crew. She has criticized the book's accounts of the Tarahumara people for "romanticizing" their lifestyle and for not adequately describing their poverty.
In July 2010 Shelton won the Deseret News Marathon in a time of 2:54:23. She says that she finds marathons more challenging to run than ultramarathons. Shelton has said that she intends to run more marathons and shorter races, citing a desire to run faster races. She is sponsored by Patagonia and competed in the 2012 U.S. Olympic Marathon Trials, but suffered a hamstring injury and did not finish.
She has set the record for the fastest female 100 mile trail race.
- Sports Chat 13, Mail Tribune (Ashland Oregon). 21:00
- McDougall, Christopher (July 2009). "Ultramarathoner Jenn Shelton". Outside. Retrieved 27 April 2010.
- McDougall 2009, p. 147
- McDougall 2009, p. 146
- Sports Chat 13 24:50
- McDougall 2009, p. 132
- Sports Chat 13 8:30
- http://pages.frederick.com/frederickmarathon.htm/ (Retrieved 9 April 2014)
- https://www.flickr.com/photos/areaguides/487061675/in/set-72157600184283007/ (Retrieved 9 April 2014)
- Thomas, Sarah (24 July 2010). "Jenn Shelton wins women's Deseret News Marathon with run of 2:54.23". The Deseret News. Retrieved 14 February 2011.
- Sports Chat 13 2:30
- Sports Chat 13 22:00
-  USATF - 2012 U.S. Olympic Team Trials - Marathon Eligibility List
- Sports Chat 13 8:20
- http://runningmegleg.com/2012/01/30/2012-olympic-marathon-trials/ (Retrieved 9 April 2014)
- http://www.flotrack.org/article/9835-FULL-RESULTS-Houston-2012-USA-Olympic-Marathon-Trials#.U0VbdvldXTo (Retrieved 9 April 2014)
- Chase, Adam (November 2009). "How the West Was Won". Running Times. Retrieved 16 February 2011.