The 19-year-old Serbian spent the second half of last season with the German club, who had the option to make the deal permanent for an initial £9.5m this summer.
But they have instead opted to negotiate another loan deal, this time for the entire 2025-26 campaign, with the purchase agreement still in place.
Nedeljkovic, who signed for Villa from Red Star Belgrade in January last year, made 10 appearances in all competitions for Unai Emery’s team during the first half of last season.
Yet eight of those were off the bench and his chances of first-team football were reduced by the signing of Andres Garcia from Levante during the last transfer window.
Nedeljkovic made 11 appearances for Leipzig during his previous loan spell and though the Bundesliga club did not want to make the deal permanent, they were keen to take him back on loan.
“I'm very happy to be able to wear the RB Leipzig jersey again next season,” said Nedeljkovic. “The club has given me a sense of trust and belonging from day one.
“I've also been able to develop well over the past few months. That's why it's a huge motivation for me to give my all to help us achieve our goals together in the new season.
“I'm excited to be back and will give it my all right from the start."
Nedeljkovic’s exit continues what has largely been a summer of departures at Villa with another young right-back, Kaine Kesler-Hayden, having joined Coventry in a deal which could eventually be worth nearly £5m.
Villa also terminated the contract of playmaker Philippe Coutinho a year early to allow him to join Vasco da Gama permanently.
Left-back Alex Moreno and midfielder Leander Dendoncker, both of whom spent last season away on loan, have also been told they can find new clubs.
Teenage forward Zepiqueno Redmond is Villa’s only new arrival to date, though the club are on course to complete the signing of goalkeeper Marco Bizot from Brest.