While at Auburn, Peirsol trained under David Marsh, Dorsey Tierney and the late Ralph Crocker.

In 2006 and 2007, Peirsol also trained with Club Wolverine at the University of Michigan along with teammates Erik Vendt, Michael Phelps, Klete and Kalyn Keller, and Kaitlin Sandeno under Bob Bowman and distance expert Jon Urbanchek.

In 2006, Hayley became the third woman in history to ever break 16 minutes in the 1500 meter freestyle, the other two women being Janet Evans and Kate Ziegler.

In 2016 she moved to Costa Rica where she was the lead teacher in a start-up Waldorf School in Lake Arenal, and did youth work in Nosara, teaching children about ocean safety and environmental awareness.

Her brother, American backstroker Aaron Peirsol, is a multiple Olympic Games gold medalist, having competed in Greece, Australia and China.