22 Nov. 1754, elected a bencher on 29 Jan. 1762, reader in 1769, and treasurer in 1770. Though he was never a hard student, he appears to have usually spent the morning hours in reading, and in the evening frequently strayed no farther from his chambers than Nando's coffee-house, in the immediate vicinity of Temple Bar.
The ascription to him of an anonymous pamphlet, published in 1760, entitled ‘A Refutation of the Letter to an Hon. Brigadier-general [George Townshend, first marquis Townshend [q. v.] ], commander of His Majesty's forces in Canada,’ is merely conjectural (Notes and Queries, 3rd ser. iii. 121).
At the bar Thurlow is said to have first distinguished himself by the spirit and address with which, in an unreported case of Robinson v. Lord Winchilsea, before Lord Mansfield at the Guildhall in 1758, he discomfited Fletcher (afterwards Sir Fletcher) Norton [q. v.], who thought to silence him by browbeating. He argued for the defendant in the great copyright case of Tonson v. Collins, before Lord Mansfield in the king's bench in Trinity term 1761 [see Tonson, Jacob], and in Hilary term 1762 received from Lord Northington the premature distinction of a silk gown. It is likely that this early advancement was due to the interest of Thomas Thynne, third viscount Weymouth [q. v.], through which Thurlow was returned to parliament for Tamworth on 23 Dec. 1765 (Hist. MSS. Comm. 11th Rep. App. iv. 401). He retained the seat until his removal to the House of Lords, and was elected recorder of the borough on 11 Oct. 1769.
The decisive turn in Thurlow's affairs is traditionally ascribed to a lucky chance. The cause célèbre of Douglas v. Hamilton, on which depended the succession to the Douglas estates, was decided by the court of session (15 July 1767) on an array of minute circumstantial evidence. Thurlow studied the case with care, and expressed in Nando's coffee-house a strong opinion that the decision was erroneous. This was overheard by some of the appellants' agents, and led to his being retained for the appeal. On 14 Jan. 1769 he fought a duel in Hyde Park with the Duke of Hamilton's agent, Andrew Stuart [q. v.], who had demanded satisfaction for some severe reflections which Thurlow had made upon his conduct. On 27 Feb. the House of Lords reversed the decision of the court of session (St. James's Chron. 17 Jan. 1769; Scots Mag. 1769, pp. 107 et seq.).
In the House of Commons Thurlow's first reported speech was on the question raised by Wilkes's expulsion, viz. whether a mere vote was adequate for the purpose. In support of the affirmative Thurlow referred to the vote of 11 April 1614, by which it was determined that no future attorney-general should sit in the House of Commons, a precedent followed in the subsequent parliaments of 1620–1 and 1625–6 by the exclusion of Sir Thomas Coventry and Sir Robert Heath (Comm. Journ. i. 316, 324, 456–60, 513, 817).
Appointed solicitor-general, 30 March 1770, Thurlow acted with the attorney-general, Sir William De Grey (afterwards Lord Walsingham) [q. v.], in the prosecution of the printers and publishers of ‘Junius's Letter to the King’ [see Almon, John; and Woodfall, Henry Sampson]. In the House of Commons (27 Nov. and 6 Dec. 1770) he increased his reputation by his able defence of the practice of issuing informations for libel by the attorney-general ex officio, and Lord Mansfield's direction to the juries in the recent cases [see Murray, William, first Earl of Mansfield]. He succeeded De Grey as attorney-general on 26 Jan. 1771, stoutly maintained the privilege of the House of Commons in the affair of the lord mayor Brass Crosby [q. v.] and Alderman Richard Oliver [q. v.], and was placed on the secret committee charged with the investigation of the attendant circumstances (28 March). He was a member of the select committee on East Indian affairs elected on 16 April 1772, and by his opposition to the clause which left the nomination of the judges to the directors contributed to the defeat of the East India Judicature Bill (18 May). He was also a member of the committee for drafting the East India Bill of the following year, supported the parliamentary inquiry into the administration of Lord Clive, and urged that it should be conducted without regard to the rule of law which excuses a witness from answering questions which tend to criminate him (Parl. Hist. xvii. 854, 870, 880).
The reasoning by which, on appeal to the House of Lords in the great copyright case of Donaldsons v. Becket (February 1774), he overthrew Lord Mansfield's doctrine of perpetual copyright at common law was unimpugnable; but in opposing the legislative settlement of the question he evinced an illiberal spirit. He has been censured for supporting (17 Feb. 1774) the motion for compelling the attendance of compositors to give evidence at the bar of the House of Commons as to the authorship of the letter to the speaker imputed to John Horne, afterwards Horne Tooke [q. v.]; but if the house was to assume the functions of a court of justice, it was manifestly desirable that
