In 741, Charles Martel died, and in this year the most important phase of Boniface's career started, with Lullus as his closest assistant. Many of the biographical facts about Lullus derive from the Boniface Correspondence: he is attested as a deacon in 745-46, as Boniface's archdeacon in 746-47, and as priest in 751 though he was probably ordained before that. The correspondence evidences that Lullus was trusted enough to be Boniface's messenger (he went to Rome twice on his behalf) and this includes the secret negotiations over Boniface's successor at Mainz. Lullus exchanges letters (and gifts) with Edburga of Minster-in-Thanet and Leoba, among others; while he may not have been the most important person in Boniface's life, but as the youngest of his associates and not yet tied to a specific place, he grew to be his closest associate. Moreover, a study by Michael Tangl, cited by Theodor Schieffer, suggests that Boniface, whose eyesight had begun to fail him early in the 740s, may have used Lullus's services in reading and writing the letters that were such an important part of his work, and Tangl suspected that Lullus likely cooperated with Boniface on some of the most important letters.