He made the first ascents of some of the United States' hardest sport routes (as of 2008) including Kryptonite (5.14c/d) and Flex Luthor (5.15a) at the Fortress of Solitude, Colorado.

In May 2004, he completed the first free ascent (FFA) of Dihedral Wall.
In 2005, he and Beth Rodden—swapping leads—made the third and fourth free ascents of The Nose.
Two days later, on October 16, Caldwell free-climbed The Nose in less than 12 hours.
A few days later, Caldwell climbed The Nose in 11 hours, descended the East Ledges, and then climbed Freerider, topping out 12 hours later – the first ascent of two El Capitan free climbs in 24 hours.
On El Capitan, Caldwell has also free-climbed: Lurking Fear, Muir Wall, West Buttress, Salathé, Zodiac, Magic Mushroom, The Dawn Wall, and New Dawn.

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

Their 19-day ascent of the Dawn Wall was considered by some as the hardest successful rock climb in history.

The following year Czech climber Adam Ondra free climbed the Dawn Wall in 8 days.
Ondra praised Caldwell and Jorgeson saying, "Tommy and Kevin put so much effort into the climb and faced so many question marks and logistical problems that I cannot really compare my effort to theirs.
I had it prepared, had all the knowledge.
I knew it was possible".
He made the first ascents of some of the United States' hardest sport routes (as of 2008) including Kryptonite (5.14c/d) and Flex Luthor (5.15a) at the Fortress of Solitude, Colorado.
In May 2004, he completed the first free ascent (FFA) of Dihedral Wall. In 2005, he and Beth Rodden—swapping leads—made the third and fourth free ascents of The Nose. Two days later, on October 16, Caldwell free-climbed The Nose in less than 12 hours. A few days later, Caldwell climbed The Nose in 11 hours, descended the East Ledges, and then climbed Freerider, topping out 12 hours later – the first ascent of two El Capitan free climbs in 24 hours. On El Capitan, Caldwell has also free-climbed: Lurking Fear, Muir Wall, West Buttress, Salathé, Zodiac, Magic Mushroom, The Dawn Wall, and New Dawn.
In January 2015, Caldwell and Kevin Jorgeson completed the first free climb of the Dawn Wall of El Capitan in Yosemite National Park, after six years of planning and preparation.
Their 19-day ascent of the Dawn Wall was considered by some as the hardest successful rock climb in history.
The following year Czech climber Adam Ondra free climbed the Dawn Wall in 8 days. Ondra praised Caldwell and Jorgeson saying, "Tommy and Kevin put so much effort into the climb and faced so many question marks and logistical problems that I cannot really compare my effort to theirs. I had it prepared, had all the knowledge. I knew it was possible".
Tommy Caldwell