The 23-year-old midfielder revealed on Wednesday how he had been in contact with Mané and manager Jürgen Klopp before committing his future to the Merseyside club.
He admitted that the Liverpool pair had been influential in his decision to join the club in an interview shortly after it was confirmed Keïta would wear the number eight shirt next season.
The details of their conversations were never discussed by Keïta, but Joyce revealed that Mané - who has the same agent as Liverpool's incoming midfielder - was instrumental in "selling the vision" in a way which the Bundesliga champions couldn't.
Mané and Keïta were both teammates at RB Salzburg, although the Africain pair saw their time together cut short when the Senegalese winger moved to Southampton in 2014, having made just two appearances together in the Austrian Bundesliga.
Joyce explains in his article for the Timeshow, despite spending a number of years apart, the two reconnected when Keïta was being linked with a move away from RB Leipzig, who he first joined in 2016.
Mané is believed to have spoken in glowing terms about Liverpool during the same time the Guinea midfielder was being tipped to join Bayern Munich. The 26-year-old claimed that the Reds had kept the promises that they made to him upon moving to Anfield, adding that Klopp's tactics would help Keïta develop as a player.
The year-long sales pitch swayed Keïta so much that Leipzig were forced to almost half their asking price for the midfielder, eventually agreeing to sell the Guinean for just over £50m. The 23-year-old will officially become a Liverpool player on July 1.