Jardim’s initial four-year spell in charge of the principality club was ended in October 2018 following a poor start to the season, and was replaced by former Arsenal striker Thierry Henry.
Henry failed to galvanise Monaco before he was sacked after just three months later, and Jardim was re-appointed in January 2019.
Jardim led Monaco to the Ligue 1 title in the 2016/2017 season, their first since 2000, and also took them to the semi-finals of the UEFA Champions league that same season.
Monaco’s performances this season have been mixed, with the club sitting 7th on the Ligue 1 table, 17 points adrift leaders Paris Saint Germain.
Moreno qualified Spain for EURO 2020 after taking charge in June but was replaced by Luis Enrique after qualification was sealed.
"We are very pleased to announce the arrival of Robert Moreno," Monaco vice president Oleg Petrov told the club's website.
"On behalf of President Dmitry Rybolovlev, I would also like to thank Leonardo Jardim for all the work accomplished and all the successes achieved in recent years."
"Leonardo and his staff did their utmost to keep the club in Ligue 1 last season, then give the team the place it deserves in our championship. We wish him good luck for the future."
Moreno’s first Ligue 1 game in charge of Monaco will be against champions PSG after the winter break.
