He found this an irksome position, and in 1718 applied to succeed Eliot of Minto on the bench, but the place was already given to Sir Walter Pringle.
He spoke against the Government in the Dunkirk debate on 12 February 1730 and also in 1730 promoted a bill to give the court of session the power of adjourning.
[5] After his return unopposed at the 1734 British general election, he was the chief adviser of the opposition formed of representative peers and members of parliament against the administration of Scotch affairs adopted by Lord Ilay.
With Erskine of Grange, he joined with the opposition in an attack in both Houses on the methods which the Government had used in the recent election of Scottish representative peers.
On 10 June 1737, Dundas was appointed a judge of the court of session, in succession to Sir Walter Pringle of Newhall, and vacated his seat in the House of Commons.
After a vacancy of nine months, the ministry and independent Whigs, overrode the Duke of Argyll's opposition, and on 10 September 1748 Dundas succeeded Duncan Forbes of Culloden as lord president, and filled the office for the rest of his life.
[3] Dunas's most famous case was his defence of James Carnegie of Finhaven in 1728 on his trial for the murder of Charles, earl of Strathmore, whom he killed in a drunken brawl by mistake for Lyon of Bridgeton.
Dundas forced the court to return to the older course, and the jury found Carnegie not guilty, and this practice was adopted in subsequent cases.