After matriculating at Magdalen Hall, Oxford, on 14 March 1672–3, he migrated to Wadham College where he was elected scholar in 1674, and fellow in 1678.

[1] On 17 January 1710 Pratt was assigned, with Sir Simon Harcourt, as counsel for Henry Sacheverell, but declined to act.

On 20 December 1711 he appeared before the House of Lords in support of the patent conferring an English dukedom on James Douglas, 4th Duke of Hamilton.

Meanwhile, on Lord Cowper's recommendation, he was raised to a puisne judgeship in the court of king's bench, and was sworn in accordingly on 22 November 1714 and knighted.

[1] On the question of prerogative submitted to the judges in January 1718, whether the custody of the royal grandchildren was vested in the Prince of Wales or the king, Pratt concurred with the majority of his colleagues in favour of the Crown.

He succeeded the latter, 15 May, as lord chief justice of the court of king's bench, being sworn of the Privy Council on 9 October.