In August 2020, Aaronson signed a homegrown contract with the first team beginning in 2021.[4] In May 2021, he made his first team debut with the Union as a substitute in a 3–0 win over the Portland Timbers.[5] Aaronson earned his first start for the Union in August where he scored the Union's equalizing goal against the New England Revolution.[6] His debut goal earned him the league's Goal of the Week honor.[7]
Eintracht Frankfurt
On November 17, 2022, it was announced that the Philadelphia Union and Bundesliga club Eintracht Frankfurt had reached a deal for the transfer of Aaronson. The fee of the deal was reported to be in the region of $4 million (plus add-ons), with a sell-on percentage for the Union also included.[8] On March 19, 2023, Aaronson made his Bundesliga debut, being subbed on in the 82nd minute in a 2–0 loss against Union Berlin.[9]
Loan to Vitesse
On January 31, 2024, the deadline day of the winter transfer window, Aaronson joined Dutch club Vitesse on loan for the rest of the season.[10] Though only playing the last 14 out of the 34 league games for Vitesse, he became the second top goalscorer, with 4 goals, behind Marco van Ginkel with 7 goals. Aaronson was seen as one of the better players of Vitesse in the 2023-2024 season, causing FC Utrecht, among other clubs, to gain interest in him.[11]
Loan to Utrecht
On June 21, 2024, Eintracht announced that Aaronson had extended his contract with the club until 2028,[12][13] and would subsequently join Dutch side Utrecht on loan for the entire 2024–25 season.[13][14]
Aaronson was, together with his FC Utrecht teammate Taylor Booth, also called up for the United States soccer team on the 2024 Olympics, appearing four times and scoring twice, in the game against New Zealand, which ended in a 4-1 victory for the United States.
