Nyland, 35, arrives on a free transfer after his contract at Sevilla expired, signing fresh terms that run until 2028.
It is his second stint at RB Leipzig, having previously spent the 2022-23 season with the club, when he made three appearances and won the DFB-Pokal, before moving on to Sevilla, where he made 27 appearances in his first season and went on to establish himself as first choice ahead of Marko Dmitrović.
He joins fresh off helping Norway reach the quarter-finals of this summer's World Cup, underlining the international pedigree Leipzig were seeking to add to their goalkeeping department; he has 48 senior caps for his country.
Sporting director Marcel Schäfer explained the thinking behind the move: "With Örjan, we're gaining a very experienced goalkeeper we already know well, both as a player and as a person.
"He showed during his first spell with us that he's an absolute team player, a reliable professional, and always ready to take on responsibility."
Despite wearing the number one shirt, Nyland arrives as competition and backup for Maarten Vandevoordt rather than as a guaranteed starter, providing depth and a senior voice in the dressing room following Gulácsi's departure to Villarreal after eleven years at the club.
Standing 1.92m, Nyland brings a wealth of experience from spells in England with Aston Villa, Norwich, Bournemouth and Reading, in addition to his previous stint in Germany, and trained with his new team-mates for the first time on Tuesday morning at Leipzig's training camp in Saalfelden, Austria.