Elia Diodati was born in Geneva in 1576 to a Protestant family originally from Lucca. Subsequently he settled in France, where he was appointed as an advocate of Parliament.

Diodati met Galileo around 1620 during one of his trips to Italy and established lifelong ties with him, maintaining contact through an intense correspondence and helping Galileo on a number of sensitive issues.

Diodati had taken it upon himself to spread Galileo's theories throughout Europe. The letters, among other things, which this great intellectual addressed to the major exponents of European culture helped Galileo's thought take root on the international scene. His contacts with Grotius (1583-1645) and Mersenne (1588-1648) exemplify the network of relationships in which Galileo found himself placed.

In a letter to Grotius dated August 15, 1636, Galileo defined Diodati as "my most cherished and true friend", and he considered him so always, opening his heart to him in such dramatic moments of his existence as the death of his daughter and the permanent loss of his eyesight.

From the very beginning of their friendship Diodati had offered himself as go-between for the publication of Galileo's works outside of Italy, as we can see in this letter of August 27, 1620: "[…] if local regulations there cause delays in the printing we can get around them here".

Finally, Diodati was the first in France to receive a copy of the Dialogo sopra i due massimi sistemi del mondo [Dialogue concerning the Two Chief World Systems] (Florence, 1632) and he arranged for its translation into Latin by Mathias Bernegger (1582-1640).

His ties to Galileo, to whose thought he was dedicated, did not end with the latter's death. In fact Diodati maintained contact with Vincenzo Viviani, to whom he handed over original manuscript materials for a projected edition, never realized, of Galileo's complete works.

He died in Paris in 1661.