The Nigerian spent 10 years at Stamford Bridge, working as technical director since 2011, playing a key role in the development of Chelsea's first team and academy.
And Emenalo is excited by his new venture with the Ligue 1 champions.
"This is a wonderful opportunity for me in a high-quality project," he told Monaco's official website.
"AS Monaco has shown great progress for several seasons and I am convinced that the future will be just as ambitious.
"[Executive vice-president] Vadim Vasilyev's willingness to see me join AS Monaco was decisive and, for me, the choice was natural after my decision to leave Chelsea."
Chelsea were also successful at youth level during Emenalo's tenure, with the club winning the FA Youth Cup six times in eight years and emerging triumphant in the UEFA Youth League on two separate occasions.
And Vasilyev is delighted to bring Emenalo in, adding: "I am very happy to be able to count on him in Monaco. I invested a lot in his appointment.
"His know-how in detection and recruitment, as well as the technical experience acquired in one of the most successful clubs in recent years, are the reasons that led us to present this ambitious challenge.
"This appointment is another sign of our ambition and our desire to be as competitive as possible."
Emenalo was reported to have had a frosty relationship with Chelsea boss Antonio Conte, which is thought to have sped up his departure, although the Italian stated he was sad to see him go when discussing his departure this month.