The 20-year-old previously represented Les Parisiens for three years between 2019 and 2022, having ended a nine-year stint with Barcelona's academy to make the move to Paris.
Simons established a reputation as one of the most promising youngsters in Europe during his time at PSG, registering four goals and six assists in seven matches during the 2021-22 UEFA Youth League.
However, the Netherlands international played just 11 times for the first team - registering one assist - and he left on a free transfer for PSV Eindhoven last summer.
While under the tutelage of Ruud van Nistelrooy, Simons began to fulfil his potential and registered an impressive 22 goals and 12 assists from 48 appearances in all competitions, including 19 strikes in the Eredivisie.
Simons's performances had reportedly attracted the attention of Arsenal, but PSG inserted a buyback clause into the Dutchman's deal, supposedly set at a mere €6m (£5.2m).
Following his breakthrough campaign, the Ligue 1 champions unsurprisingly chose to exercise their buyback option, and PSV confirmed on Sunday that Simons had left their training camp to finalise his return to PSG.
Now, Luis Enrique's side have confirmed the return of Simons on a four-year contract until the 2026-27 season, and he will continue his development on loan with Leipzig for the upcoming campaign.
Speaking to the official Leipzig website, Simons said: "The Bundesliga is one of the best leagues in Europe and RB Leipzig are one of the best teams in the Bundesliga.
"Coming to Leipzig is the right step for me because RBL constantly show how to develop young players and be successful with them.
"I'm joining a club that regularly plays Champions League football. The squad has the perfect mix of lots of young and experienced players, and the whole club is hungry for success.
"I was immediately impressed by RB Leipzig's style of play and I strongly believe that my qualities will be a good match for this team and we can achieve a lot together. I can hardly wait to play with my new teammates and to start the new season. Leipzig - I can't wait!"
Comfortable in a variety of positions across the forward line, Simons was deployed as a left-winger, right-winger, attacking midfielder and centre-forward with PSV, winning the KNVB Beker and Dutch Super Cup.
The Netherlands international becomes PSG's seventh new arrival of the summer window, following Cher Ndour, Lee Kang-in, Milan Skriniar, Marco Asensio, Manuel Ugarte and Lucas Hernandez to the Parc des Princes.
Simons makes the move to Leipzig just one day after the German giants dipped into the PSG ranks to sign 18-year-old defender El Chadaille Bitshiabu on a permanent deal.