He was a founding member of the Paris Foreign Missions Society and became a missionary in Asia.

He was ordained a priest on 27 December 1655[1] and was recruited by Alexander de Rhodes, SJ, as a secular clergy volunteer to become a missionary in Asia, together with François Pallu and Ignace Cotolendi.

[2][3][4] On 29 July 1658 Pope Alexander VII appointed him as the first Apostolic Vicar of Cochin and as titular bishop of Beirut.

[1] On 11 June 1660 he was consecrated bishop by Victor Le Bouthillier, Archbishop of Tours.

[5] Bishop Lambert left Marseilles on 26 November 1660 accompanied by Fathers De Bourges and Deydier,[6] and reached Mergui in Siam 18 months later.