Tallis' earlier life is not well documented, though it is known he was employed as an organist at an Abbey at the time of the dissolution of the Monasteries in England. He later took up a post in the Chapel Royal working in succession for Henry VIII, Edward VI, Queen Mary and then Queen Elizabeth I. This was obviously a period of substantial change in religious customs, and as a catholic like the younger William Byrd who joined him at the Chapel Royal, Tallis would have had to serve the requirements of the church according to the prevailing religious climate.
Among the works produced by Tallis there are a number of hymns which can still be found in hymn books today, including his canon universally known as Tallis' Canon, and the imaginatively named "First Mode Melody", "Third Mode Melody" and "Fifth Mode Melody". The "modes" referred to were roughly equivalent to a set of scales begining on different white notes of a keyboard, but because the tuning of the notes was based on exact frequency ratios rather than today's method based on the well-tempered compromise, each scale or mode sounded quite unique in colour rather than like the same scale transposed. Tallis' Third Mode Melody in particular is well known by virtue of its use by Ralph Vaughan-Williams in his "Variations on a theme by Thomas Tallis" which in turn has featured in films such as "Master and Commander: The Far Side of the World".
To find out more about these works mentioned above, here is some Thomas Tallis music available on mfiles:
A number of groups have specialised in music of the Renaissance Period such as the Tallis Scholars under their director Peter Phillips. There are a number of recordings available by these groups such as the following: