John Sheppard was a sixteenth-century English composer and organist. He is considered one of the better composers of the Tudor period. Little is known about his early life. He appears in English records in 1554, when he applied, probably unsuccessfully, for the degree of Doctor of Music at Oxford University based on his life experience and study as a composer. In late 1543 he was appointed to the position of informator choristarum at Magdalen College, Oxford. He remained there for five years and next appears in the Oxford record as holding the position of Gentleman of the Chapel Royal. Historian David Chadd discovered that Sheppard recorded a will in early December 1558 and that he was buried later the same month. However, he appears in English records again as having been granted liveries for the coronation of Elizabeth I in January 1559. It is unclear whether his date of burial is incorrect or if the livery list for the coronation was created before his death and never altered.

Most of Sheppard's musical contributions, which were preserved, are from the reign of Mary Stuart (Mary I, or "Bloody Mary"). He may have played an important role in supplying Mary's Royal Chapel with elaborate works for the Sarum Rite, which Mary restored (along with the Catholic Church in England) upon her accession in 1553. Most of Sheppard's surviving music is found in the Sarum Rite. However, he also wrote for the Church of England rite during the brief reign of Edward VI. Shepperd's fifteen English anthems are well suited for the piety and simplicity required by Protestant reformers. Additionally, he wrote at least two secular songs, "O happy dames," and "Vain, vain, all our life we spend in vain."

Music historians struggle today to pin down Sheppard's contributions to sixteenth-century music and the Tudor period in general, even though several of his contemporaries have been promoted in later centuries. Much of his work has not survived to the present day, and that which is known is largely incomplete. Among music historians, Shepperd's style is said to be instantly recognizable, since he favored an unusual six-part harmony. He may have felt that such an approach added to the gravity of worship. In recent years, Shepperd's music has been recorded and produced in a CD format. According to critic Peter Philips, Shepperd's Sarum Rite "begins with some of the most haunting words...'Media vita in morte sumus' (in the midst of life we are in death)."