His elder brother, Rolf, had died in 1882 and his mother in 1886 and so in 1905 (as the nearest heir) he inherited the barony of Lucas and the lordship of Dingwall (which are able to pass through female lines) from his maternal uncle, the 7th Earl Cowper.

He was Under-Secretary of State for the Colonies between March and October 1911 and then served as Parliamentary Secretary to the Board of Agriculture and Fisheries from 1911 to 1914.

He was sworn of the Privy Council in 1912[4] and in August 1914 he entered the cabinet as President of the Board of Agriculture and Fisheries.

Lucas also played a prominent part in David Lloyd George's Land Campaign.

On 3 November 1916, whilst flying over German lines in the vicinity of Bapaume, his aircraft was attacked and brought down by a German fighter-aeroplane, and Lucas died of wounds whilst a prisoner of war the same day at the age of 40 years.