- At 15, he became the youngest American to break two minutes in the 200m backstroke; captured a silver medal in this event two years later at the 2000 Olympics.
- Has a tattoo of the Olympic rings on his lower right hip; he got it during the 2000 games in Sydney.
- In 2003, he and younger sister Hayley became the only sibling duo to medal at the same World Championships.
- Prior to collecting three gold medals at the 2004 Olympics, he bypassed his final year of collegiate eligibility and agreed to a multi-year endorsement contract with Nike.
- Attended the University of Texas with fellow Olympians Brendan Hansen and Ian Crocker; the three swam together (with Jason Lezak) in the 4x100m medley relay in Athens in 2004.
- A spokesman for the oceanic protection group Oceana, he launched a companion website called racefortheoceans.com, where supporters can pledge money for Oceana's efforts.
- Hayley Peirsol — Sister
- Erin Hartig — Stepsister
- Greg Hartig — Stepbrother
- Tim Hartig — Stepfather
- Louella Peirsol — Mother
- University of Texas, Austin, Texas, United States (2007)