After a week in which he turned 18, made his international debut for the United States and scored his first goal for his country, Reyna has agreed fresh terms at Signal Iduna Park.
The midfielder arrived from New York City in 2019 and since establishing himself in Dortmund's first team in January he has scored four goals and supplied six assists in 30 appearances in all competitions.
"BVB are a big club that can challenge for titles and are in all the important competitions. Young players in particular have the chance to develop here," said Reyna.
"I have already learned a lot in Dortmund and I want to learn a lot more in the future. I look forward to being with BVB in the long term."
Sporting director Michael Zorc added: "Gio's development in recent months has been incredible. He will definitely be an important part of Borussia Dortmund's sporting future.
🎙️ Lucien Favre:— Borussia Dortmund (@BlackYellow) November 20, 2020
"It's a great thing for Borussia Dortmund to have a player like Gio, he has a lot of potential. If he continues like this, then he'll be an extremely important player for BVB throughout the future. pic.twitter.com/3CgC9Acij7
"I am personally very pleased that he has decided to extend his contract with BVB in the long term with complete conviction."
Reyna became the first 17-year-old to record three assists in a single Bundesliga match since records began in 1992 during the 4-0 victory over Freiburg on October 3.
He found the net with a free-kick in the USA's 6-2 victory over Panama on Monday, becoming the third-youngest goalscorer in the country's history at 18 years and three days old.