He obtained a position as chamberlain to Cardinal William Allen, and left for Rome on 11 July 1592 (It was once thought that Tregian encountered the composer Peter Philips who was serving William Allen in Rome. But Philips's stay in Rome was from 1582 to 1585, well before Tregian graduated the English College at Douai.) On Allen's death in 1594 Tregian appears to have gone to Brussels. A document from 1603 acknowledges Tregian as "being with the Archduke" there (the archduke being Archduke Albert). In an attempt to find a musical association, Persons notes that composer Peter Philips was the court organist to Archduke Albert from 1597 until after 1610 and that during the time Tregian was also associated with the Archduke, the two might have come into contact.