The former striker has landed his third job in management following a playing career in which he became an Ireland and Tottenham legend.
Keane first took charge of Indian side ATK FC in a player-manager role in 2018 before moving to Maccabi Tel Aviv five years later.
He won the Israeli Premier League in his only season at the club before departing last June.
Ferencvaros announced on Monday that Keane has become their new head coach.
"The new head coach arrived in Budapest on Sunday evening and will leave on Tuesday to join our team at the training camp in Spain," they said.
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Keane has replaced Pascal Jansen, who was Liverpool boss Arne Slot's assistant at AZ Alkmaar and is set for MLS side New York City FC.
Amongst the Ferencvaros squad is midfielder Naby Keita, who has joined the club on loan from Werder Bremen.
The 29-year-old established himself at RB Leipzig before signing for Liverpool in 2018 after they activated his £48million release clause.
Keita won the Premier League and the Champions League alongside various other honours during his career at Anfield.
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However, various injury issues meant he was unable to be a consistent starter for Liverpool, making 129 appearances across five seasons.
The Guinean signed for Bundesliga outfit Werder Bremen in 2023, but once again struggled to maintain his fitness.
Keita was fined and banned from the first team in April after he took to social media to reject claims he went home after a squad omission.
He hasn't played for the club since, but looks set to make his return to the football pitch with Ferencvaros under Keane.
Ferencvaros are currently second in the Hungarian top-flight, the Nemzeti Bajnoksag I.
They're just a point behind leaders Puskas Akademia FC and have a game in hand at the halfway stage of the season.
Keane's new club are also 16th in the UEFA Europe League league phase in which they hosted Spurs on matchday two.