The midfielder joins Eintracht in January on a contract until 2027.
In July 2020, Aaronson played his first match for Philadelphia Union's YSC Academy then got promoted to the senior side. He signed a contract and played his first official game coming on as a substitute, in May 2021.
He then was then signed in November 2022 by Eintracht for around $4 million (plus add-ons).
"In Paxten Aaronson we've signed a much sought-after and very talented player who will give our attack even more flexibility in the future," said Eintracht Frankfurt board member for sport Markus Krösche.
"We have a clear plan for him and want to build him up carefully. We'll give Paxten all the time necessary to get used to his new surroundings and to develop in the best possible way," Krösche added.