Falconieri was born in 1585 in Florence, the tenth of the thirteen children of Paolo Falconieri and his second wife Maddalena degli Albizzi.
At a young age he went to Rome and became an advocate at the Roman Curia and papal prelate during the pontificate of Pope Paul V. In 1619 he became Governor of San Severino and a referendary of the Tribunals of the Apostolic Signatura of Justice and of Grace.