Caldwell made the first free ascents of several major routes on El Capitan in Yosemite National Park.

[1] He made the first ascents of some of the hardest sport climbing routes in the U.S., including Kryptonite at 5.14d (9a) in 1999, and Flex Luthor at 9a+ (5.15a) in 2003, both at the Fortress of Solitude in Colorado.

[2] In 2015, National Geographic called Caldwell "arguably the best all-around rock climber on the planet",[3] and he is an important figure in the history of the sport.

[5][6] Caldwell and three fellow climbers Beth Rodden, John Dickey, and Jason 'Singer' Smith were held hostage for six days by rebels in Kyrgyzstan in August 2000.

[15] In February 2022, Caldwell fell while projecting Magic Line, a 5.14c (8c+) trad route in Yosemite National Park, tearing his Achilles tendon as he struck the wall, requiring a full reconstruction.

[17] Foregoing surgery, he restarted his recovery process, following his doctor's orders more strictly, before tearing his Achilles once more during a physical therapy session, requiring another reconstruction.

[16][17] He made the first ascents of some of the United States hardest sport routes including Flex Luthor in 2003 at the Fortress of Solitude, in Colorado, which remained unrepeated for 18 years, before getting its first repeat by Matty Hong in October 2021, who suggested a possible grade 5.15b (9b), but was regraded to 9a+ (5.15a) by Jonathan Siegrist in 2022.

[1][19] In January 2015, Caldwell and Kevin Jorgeson completed the first free climb of The Dawn Wall on El Capitan in Yosemite National Park, after six years of planning and preparation.

[2] The ascent captured global attention and earned a nod from President Barack Obama, who said: "You remind us that anything is possible", and which was made into the 2017 climbing film, The Dawn Wall.

Climbers Alex Honnold and Tommy Caldwell embark on an expedition to conquer Alaska's treacherous Devil's Thumb.