The Sounders also played in the 2023 Leagues Cup, which featured every MLS and Liga MX team, and finished third in their group behind CF Monterrey and Real Salt Lake.

[6] The choice of Providence as sponsor was criticized by fans and several organizations, including the Emerald City Supporters and the Sounders FC Alliance Council, due to the healthcare system's policies on abortion and transgender care, as well as its treatment of low-income patients.

[11] During the offseason, the Sounders exercised their contract options on most of their roster with the exception of forward Will Bruin and midfielder Alfonso Ocampo-Chavez; defender Jimmy Medranda was also released into free agency.

[15] The club's two SuperDraft picks, forward Eythor Bjørgolfsson and defender Blake Bowen, were signed by reserve side Tacoma Defiance after training with the first team.

[16] The Sounders opened their training camp at Starfire Sports in Tukwila on January 4, 2023, with a full roster of healthy outfield players following the return of João Paulo and Obed Vargas from their 2022 injuries.

[24] The team were eliminated from the tournament, but a month later qualified for the expanded 2025 FIFA Club World Cup as one of four CONCACAF entrants—all recent Champions League winners.

[35] The Galaxy cut the lead by a goal and made several unsuccessful attempts to score an equalizer; the team appealed for a penalty following an alleged handball by Nouhou in stoppage time, but were denied.

[39] After the match, Schmetzer called the result an "emotional punch to the jaw" and said that the Sounders "have to get back to understanding that this is a rivalry"; he also attributed the shift in momentum to his substitution of Léo Chú for Héber and uncharacteristic defensive mistakes.

[43] The club entered the U.S. Open Cup in the third round along with other lower-ranked MLS teams and hosted San Diego Loyal SC of the second-division USL Championship at Starfire Sports in Tukwila.

The Sounders reclaimed their two-goal lead but conceded twice—a free kick from Corona and a long-distance strike by Kyle Adams in stoppage time—to finish regulation time at 3–3.

In extra time, Reed Baker-Whiting scored from outside the box for Seattle, but San Diego's Jackson Kasanzu headed an equalizer shortly after entering as a substitute.

[44][45] The Sounders returned to MLS play with a scoreless draw against Real Salt Lake in Utah, where the team had only won once in fifteen previous regular season matches.

[46][47] Defiance defender Cody Baker was signed to a short-term contract to replace Rowe ahead of the next match at home against Sporting Kansas City, which the Sounders would play without the injured Roldan and Ruidíaz, as well as João Paulo for yellow card accumulation.

[50] A few days after their elimination from the U.S. Open Cup, the team traveled to play the Houston Dynamo with both Baker and Rothrock signing an additional short-term contract to fill in for injured first-team players.

The match was disrupted in the first half by a weather delay and included two red cards shown to Dynamo players; the sole goal in the 1–0 away victory was scored by Rothrock in the 87th minute.

[52] The Sounders returned home to play Austin FC, who snapped an eight-match winless streak with a 2–1 midweek win at Lumen Field; after several substitutions, Fredy Montero scored for Seattle in the 79th minute and the team unsuccessfully pushed for an equalizer.

[57] On June 3, the Sounders and women's team OL Reign held a doubleheader event at Lumen Field, their shared home venue, against their respective Portland rivals.

[58] The clubs sold 42,054 tickets to the doubleheader, which began with a scoreless draw between the Sounders and Timbers; it was the 100th MLS shutout for Frei and also marked the return of Cristian Roldan following his concussion.

[59] After the match, Schmezter stated that the team had "dropped points" but he "believe[d] in the process that we have" especially as players returned from injuries; the Sounders had only scored four goals over an eight-match stretch that included four losses.

[62] They returned home and played Orlando City SC to a scoreless draw to continue their month-long winless streak; Ruidíaz was absent for the match to attend a family funeral.

[67] In July and August, MLS play halted for the Leagues Cup, an international competition with Liga MX clubs hosted in the United States and Canada.

[71] The Sounders returned to regular season play on August 20 by hosting Atlanta United FC at Lumen Field under hazy conditions due to nearby wildfires.

The team lost 2–0 as Atlanta's Giorgos Giakoumakis scored in the 11th and 65th minutes to beat Stefan Frei, who had been named captain and set a new club record for appearances in all competitions with his 340th match.

[74] The Sounders then hosted the Portland Timbers in their penultimate Cascadia Cup fixture of the season; the home side took a 2–0 lead in the first half through goals by Raúl Ruidíaz and Léo Chú, who was sent off in the 53rd minute for his second yellow card of the match.

[82] St. Louis were awarded a penalty kick for a foul by Cristian Roldan on Niko Gioacchini in the 66th minute, but it was rescinded after video review due to the lack of contact.

[85] The team hosted the opening match at Lumen Field and won 2–0 with Rusnák's penalty kick before half-time and a header by Morris off Nouhou's cross in the 74th minute.

Morris scored after half-time and had another goal that was ruled offside; a foul on Ruidíaz in the 75th minute was recommended for a potential penalty kick by the video assistant referee but was not awarded.

[90] The Sounders hosted defending MLS Cup champions Los Angeles FC in the Western Conference Semifinals on November 26 and lost 1–0 after they conceded a goal to Denis Bouanga in the 30th minute.

[99] The Sounders entered the 2023 U.S. Open Cup in the third round as part of the lower tranche of MLS teams, as determined by their final position in the 2022 regular season.

[103] A base salary cap of $5.21 million applied to the non-supplemental players with exceptions for certain categories, including the club's three designated players—Nicolás Lodeiro, Raúl Ruidíaz, and Albert Rusnák—who each counted for a reduced amount.