We do not know much about Walsingham's life and work until 1380, when he identified himself as the compiler of the Liber benefactorum (London, British Library, Cotton MS Nero D VII). Before that date, an entry in the Register of Simon Sudbury, Bishop of London, mentions that a Thomas Walsingham, monk of St Albans, from the diocese of Norwich, was ordained priest on 21 September 1364. It seems likely from this evidence that Walsingham was born around 1340, and that he or his ancestors came from the town of Walsingham, in Norfolk.

Further evidence suggests that Walsingham attended Oxford before his ordination: he is included in a list of alumni of Gloucester College, the Benedictine studium. Walsingham speaks emotionally of Oxford in his Chronica maiora, when he laments the rise of Wyclifism at the university. Reacting to the occasion when several provosts and rectors debated whether they should accept a papal bull authorizing Wyclif's arrest, Walsingham writes:

As Martin Camargo notes, St Albans monks were ‘exceptionally numerous’ at Oxford: their subsequent reputation for effective composition in Latin contributed to their prominence as defenders of orthodoxy in the Wyclifite controversies. Walsingham's textuality, however, was to take another path; rather than making himself useful, he transformed established modes of monastic composition to expose the workings (and often the flaws) of public figures. Even in the very early Liber benefactorum, which should be simply a functional (if ornate) text, we see traces of the political sensibility that will develop in his later texts and ultimately prove harmful to his career.