This is a list of all seasons played by Portland Thorns FC in the National Women's Soccer League (NWSL), from their inaugural season in 2013 to their last completed season in 2022. It details their record in every major competition entered, as well as the top goalscorers for each season.

The club have won every major NWSL trophy. Portland was the first team to win three NWSL Championships, the third to win two NWSL Shields, and won the 2021 NWSL Challenge Cup. The Thorns also won the 2020 NWSL Fall Series Community Shield and 2021 Women's International Champions Cup, and Thorns players have been named the league's most valuable player twice (Lindsey Horan in 2018, Sophia Smith in 2022).

2013

Under head coach Cindy Parlow Cone, the Thorns played in the new league's inaugural game on April 13, 2013, against host team FC Kansas City, which ended in a 1–1 draw in which Christine Sinclair scored the club's first goal on a penalty kick. The team's first home match on April 21 provided the club its first victory, a 2–1 win over Seattle Reign FC. Beyond setting a new league record, the home opener crowd of 16,479 at Jeld-Wen Field eclipsed any single-game attendance from Women's Professional Soccer. Subsequently, the team's regular-season home finale of 17,619 topped the previous mark of 16,479 and also ranked at the time among the top single-game marks in women's professional soccer history in the United States.

The Thorns were also an attendance draw on the road. Portland's road games were witnessed by season-high attendance figures or sellout crowds, including a record-setting crowd at the Maryland SoccerPlex against the Washington Spirit on May 4. A total of 5,011 people were in attendance, besting the previous record for a women's game at the Soccerplex by more than 300 and about 500 more than normal capacity.

On August 28, 2013, the NWSL named Thorns FC forwards Christine Sinclair and Alex Morgan, and defender Rachel Buehler, to the league's second-team Best XI.

The club finished in a three-way tie atop the league in the regular-season standings, but by virtue of goal differential tiebreaker, the club claimed the No. 3 seed in the NWSL playoffs. In the first round of playoffs on August 24, the Thorns beat FC Kansas City 3–2 after extra time. A week later they beat the Western New York Flash 2–0 in the championship game, with Tobin Heath and Christine Sinclair scoring the two goals and the Thorns overcoming the red-card ejection of defender Kat Williamson in the 57th minute, to become the first NWSL Champions.

After the end of the season, Parlow Cone resigned as head coach on December 5, 2013. She cited personal reasons, particularly a desire to spend more time with her husband, Portland Timbers director of sports science John Cone, who also resigned around the same time.

2014

The Thorns kicked off their 2014 season with the announcement of a new head coach, Paul Riley, formerly of the Long Island Fury of the Women's Premier Soccer League. The team traded goalkeeper Karina LeBlanc to the Chicago Red Stars and replaced her with 2013 FIFA World Player of the Year recipient Nadine Angerer, and in April traded Kat Williamson, Courtney Wetzel, and a first-round pick in the 2015 NWSL College Draft to the Flash for defender Sarah Huffman and the right to sign Spanish international Verónica Boquete.

The Thorns broke the club's own NWSL attendance record with 19,123 attending an August 3 game between Portland and expansion team Houston Dash at newly renamed Providence Park. After finishing third in the regular season, the Thorns qualified for the playoffs but were knocked out in the semi-finals by FC Kansas City.

2015

The Thorns made a number of roster moves in the offseason. In November 2014, the Thorns traded Amber Brooks to the Western New York Flash to re-acquire Kat Williamson and acquire midfielder McCall Zerboni. The team also traded the 25th and 34th-overall picks in the 2015 draft to Sky Blue FC in exchange for defender Kendall Johnson, a Portland native and former University of Portland standout, and traded the 13th-overall 2015 pick and two second-round 2016 NWSL College Draft picks to the Washington Spirit in exchange for English international forward Jodie Taylor, who had played at Oregon State and was among the league's goalscoring leaders during the 2014 NWSL season.

Portland also signed Equatorial Guinea international forward Genoveva Añonman, who had made 122 appearances and scored 95 goals for in the German Frauen-Bundesliga, and midfielder Sarah Robbins from Åland United, champions of Finland's Naisten Liiga.

As part of the National Team player allocation process, Portland received Canadian international midfielder Kaylyn Kyle and defender Rhian Wilkinson.

In February, defender Nikki Marshall announced her retirement from professional soccer. In her two seasons with the Thorns, Marshall, 26, appeared in a club-record 46 consecutive regular-season matches, playing 3,943 minutes.

On June 19, 2015, the Thorns made NWSL history when goalkeeper Michelle Betos headed the equalizing goal for 10-woman Portland in the 95th minute against FC Kansas City, the first goal scored by a goalkeeper in the league. The Thorns also sold out Providence Park for the first time in a match against Seattle Reign FC following the 2015 FIFA Women's World Cup, again setting the league's attendance record with 21,144.

However, the Thorns finished in 6th place of the now 9-team league, missing the playoffs for the first and only time in its history. At the end of the season the team announced that head coach Paul Riley's contract was allowed to expire, though reports in 2021 would reveal that Riley had been investigated for alleged sexual harassment and coercion and quietly terminated.

On October 5, the Thorns hired Washington Spirit head coach Mark Parsons as head coach for the 2016 season. In December, the club brought Angerer back as its goalkeeping coach.

2016

In Parsons's first season in charge, the Thorns executed a series of trades — anchored by moving founding forward Alex Morgan and midfielder Kaylyn Kyle to expansion team Orlando Pride — that resulted in the acquisitions of defender Emily Sonnett in the 2016 NWSL College Draft, Lindsey Horan via allocation from Paris Saint-Germain, Meghan Klingenberg through as an Orlando pick-and-trade during the 2016 NWSL Expansion Draft, goalkeeper Adrianna Franch's rights from the Boston Breakers, and international slots used to sign Olympique Lyonnais Féminin midfielder and France national team Capitan Amandine Henry and Icelandic international midfielder Dagný Brynjarsdóttir, and Danish international forward Nadia Nadim acquired from Sky Blue FC. Parsons also signed former Washington Spirit winger Hayley Raso off waivers and acquired Meg Morris from Sky Blue. At the start of the 2016 preseason, only eight players from the 2015 team remained on the roster.

The acquisitions formed the core of a team that won the Thorns its first NWSL Shield in 2016, which allowed it to host its first playoff match, against a Western New York Flash team led by former Thorns coach Paul Riley. The physical match, with a playoff-record 20,086 in attendance, ended in regulation as a 2–2 draw, and the Thorns lost in a 4–3 upset after extra time.

2017

The Thorns retained most of their roster from 2016, with Kat Williamson retiring and Betos declining the Thorns' contract offer to play for Vålerenga in Norway. Heath missed much of the season with a back injury, forcing Sinclair into a deeper attacking midfield role, and Franch stepped into the starting keeper role, with the Thorns' defense leading the league in shutouts.

After a league record and 47 points for a second-place finish behind the NWSL Shield-winning North Carolina Courage, successor to the Western New York Flash team that had beaten them in the final the year before, the Thorns defeated the Orlando Pride 4–1 in a playoff semi-final. In the championship match, Portland defeated the Courage at Orlando City Stadium in a physical 1–0 match to win their second NWSL championship. Following the victory, the team held a victory rally in Providence Park.

2018

The Thorns lost Henry and Nadim to Olympique Lyon and Manchester City, respectively, as the NWSL salary cap of $315,000 for each team prevented the Thorns from offering competitive salaries. On January 11, 2018, the team announced a trade that would send midfielder Allie Long to Seattle Reign FC in exchange for the rights to Australian international defender Caitlin Foord. Long had been with the team since its inaugural season, and was one of the first players to reach 100 NWSL appearances with one club. With Long's departure, Tobin Heath and Christine Sinclair were the only remaining players from the first Thorns season.

The team signed Australian fullback Ellie Carpenter to play for the Thorns on her 18th birthday, and traded the team's previous year's top draft pick Savannah Jordan to Houston Dash for Brazilian international midfielder Andressinha. The team also acquired Boston Breakers players Margaret Purce, Ifeoma Onumonu, and Angela Salem in the 2018 NWSL Dispersal Draft.

The Thorns finished with a regular season record of and matched their second-place finish from the previous season, again finishing behind the Courage. The Thorns beat Seattle Reign FC 2–1 in the playoff semi-finals to stage a rematch against the Courage, rematch of the previous seasons final. The match drew a sellout attendance of 21,144, breaking the league playoff attendance record that the Thorns had set in the previous season. However, the Thorns lost to the Courage 3–0, and North Carolina became the first team to win the NWSL Shield and the NWSL Playoffs in the same season.

2019

Before the start of the season, the Thorns announced that the team would play its first six games on the road due to ongoing renovations and expansions of Providence Park. The Thorns lost only one of their first six games, then lost once in a nine-game stretch spanning June and July. This run included the return of several key players who had missed time for the FIFA Women's World Cup, including Lindsey Horan, the reigning NWSL MVP, and team captain Christine Sinclair. The Thorns fine form was encapsulated by a 5–0 rout of the Houston Dash on July 24. Beginning the month of September at the top of the table and contenders for the NWSL Shield, the team entered what would be the worst run of form since Mark Parsons was named head coach. Portland would lose three of their final five games, including an embarrassing 6–0 loss to the North Carolina Courage which would end up as the most lopsided loss in team history. After finishing the season with a scoreless draw against the Washington Spirit, the Thorns finished third in the league, meaning they would not host a playoff game for the first time since 2015. The Thorns would be knocked out of the playoffs after a 1–0 defeat to the Chicago Red Stars.

2020

Due to the COVID-19 pandemic, on March 12, 2020, the Thorns canceled their preseason tournament, scheduled for March 29-April 4. On March 20, 2020, the NWSL postponed the start of the league's regular season indefinitely. The Thorns participated in the inaugural NWSL Challenge Cup, defeating the North Carolina Courage in the quarterfinals but losing to the eventual champions Houston Dash in the semifinals. The Thorns also participated in and clinched the 2020 NWSL Fall Series Community Shield with a win on October 11, 2020, over OL Reign.

2021

Abuse scandal