Thomas Englefield was the second son of Sir Thomas Englefield Senior - the Speaker of the House of Commons - of Englefield House in Berkshire, by his wife, Margery, daughter of Sir Richard Danvers of Prescot and Calthorpe in Oxfordshire. His elder brother, Richard, died within his father's lifetime and so it was Thomas who succeeded to the family inheritance at the age of twenty-six in 1514.

Thomas Junior had previously selected the law as his profession and pursued his studies at the Middle Temple. Five years after his father's death, he was called upon to fill the office of High Sheriff of Berkshire and Oxfordshire and, in Autumn of 1520, he became reader at his inn of court. The next year, he was one of ten who were called to the degree of the coif and, on 3rd December 1523, he was advanced to be King's Sergeant, at the same time receiving a grant of £100 a year for life. Of his promotion to the bench as a Judge of the Common Pleas, the patent has not been found; but, though William Dugdale names him from the date of the first fine levied before him, in January 1527, it is clear from the Year Books that he sat as a judge during the previous Michaelmas. He was probably was the successor of Lewis Pollard. He was knighted at the same time.

Sir Thomas' judgments are recorded in the Year Books, showing that he performed the functions of his office until his death on 28th September 1537. To his judicial duties were added those of Master of the King's Wards, which he held in conjunction with Sir William Paulet. He was buried at Englefield, where there was once a memorial brass of him in his robes, and of his wife Elizabeth, daughter of Sir Robert Throckmorton of Coughton Court in Warwickshire. By her, he had three sons and nine daughters, one of the latter of whom was the second wife of Chief Baron Sir Edward Saunders. His eldest son, Francis, lost the paternal estate by attainder for high treason in 1592. His second son, John, seated at Vastern Manor in Wootton Basset, was the father of another Francis, who was created a baronet by King James I in 1612, a title which expired in 1822 with the death of the seventh possessor without issue.