Sesko has been highly sought-after following the 2021-2022 season, in which he scored 11 goals in all competitions – including one in a Champions League qualifier – for Austrian side Salzburg.
He previously spent time on loan at second-tier Liefering, scoring 21 goals in 29 league games, while he netted Salzburg's winner in a pre-season friendly against Liverpool in July.
Seen as the next potential star off the Austrian club's production line after Erling Haaland and Karim Adeyemi, Sesko had reportedly been drawing interest from Premier League clubs including Manchester United, Chelsea and Newcastle United.
Yet the 19-year-old Slovenia international has instead elected to join Leipzig, Salzburg's sister club.
The Bundesliga side has signed Sesko on a five-year contract that will start on 1 July next year.
Sesko explained how Leipzig's track record of improving youngsters and handing them first-team opportunities is what drew him to the club.
He told the club's official website: "RB Leipzig are one of the best clubs in Germany and are establishing themselves as one of the best in Europe year-on-year.
"A success story has been written here in just a few years and I want to be a part of it in the future.
"The club's philosophy of placing trust in young players and playing attractive, attacking football is a perfect fit for me. The city, the stadium and the whole infrastructure at RB Leipzig, as well as the many good discussions with the club, convinced me that this move is absolutely the right decision.
"My focus is now on the season with Salzburg, that I want to use to continue developing and be as successful as possible."
Christopher Vivell, Leipzig's technical director, said: "Benjamin is one of Europe's best young talents and has a great amount of potential to become one of the best."
"We've managed to pull off a brilliant transfer," said commercial director Florian Scholz. "We're very proud that Benjamin has decided to come to RB Leipzig because he had a lot of offers from other clubs and we had to beat off great competition.