2018 Portland Thorns FC season

The 2018 Portland Thorns FC season was the team's sixth season of existence. The Thorns played in the National Women's Soccer League (NWSL), the top division of women's soccer in the United States. The Thorns entered the season as defending NWSL Champions.

Off-season
On September 21, 2017, Raso signed a loan with Brisbane Roar for the 2017–18 W-League season.

on September 24, 2017, the club announced that midfielder Amandine Henry and forward Nadia Nadim will not be returning to the Portland Thorns in 2018 season. The moves were made for financial reasons, NWSL has a strict salary cap of $315,000 for each team and the Thorns could not compete with the offers made by Lyon and Manchester City.

In October 2017, Boureille was loaned to Brisbane Roar for the 2017–18 W-League season.

On October 24, 2017, it was announced that Sonnett signed a loan with Sydney FC for the 2017–18 W-League season.

On January 11, 2018, the club acquired the rights to Australian forward Caitlin Foord and a 2020 conditional natural second-round draft pick from the Seattle Reign in exchange for Allie Long.

On January 12, 2018 Portland acquired Brazilian midfielder Andressinha from the Houston Dash in exchange for forward Savannah Jordan.

On January 17, 2018, Portland Thorns FC selected midfielders Sandra Yu and Gabby Seiler and goalkeeper Bella Geist from the 2018 NWSL College Draft.

On February 15, 2018, Ashleigh Sykes announced her retirement from professional soccer.

Preseason
Thorns Spring Invitational presented by Tillamook Yogurt

First team squad
Last updated: March 27, 2018
 * (FP) = Federation player
 * (Loan) = on loan

NWSL Season Awards

 * Most Valuable Player: Lindsey Horan
 * Defender of the Year: Emily Sonnett (finalist)
 * Coach of the Year: Mark Parsons (finalist)
 * Goalkeeper of the Year: Adrianna Franch (finalist)
 * Best XI: Adrianna Franch, Emily Sonnett, Lindsey Horan, Tobin Heath
 * Second XI: Emily Menges, Christine Sinclair