In a letter to T. E. Ellis, Lewis wrote to his friend, then Chief Whip: 'I will never again fight a constituency as an official Liberal.'

With Lloyd George, Lewis was an enthusiastic supporter of Cymru Fydd, a nationalist movement within Welsh Liberalism.

At the 1918 general election he contested the new University of Wales constituency as a Coalition Liberal; He was offered a peerage on his retirement from Parliament in 1922, but declined the honour.

He was appointed a Knight Grand Cross of the Order of the British Empire (GBE) in the 1922 Dissolution Honours List.

In 1925, while walking in the hills above the town prior to a meeting of the Library's council, Lewis suffered a fall down a quarry which left him paralyzed for the rest of his life.

An active lay member of the Calvinistic Methodist Connexion, Lewis was elected Moderator of the denomination in 1925, although he declined the post.

"Lloyd George's Flintshire Loyalist: The Political Achievement of John Herbert Lewis" (PDF).