Paul Johnson, the prolific journalist, historian, biographer, speechwriter and novelist whose public conversion in 1977 from Labour Party stalwart to bulldog defender of Margaret Thatcher and conservatism made him a divisive figure in British literary circles, died on Thursday at his home in London. He was 94. His son Daniel announced the death, “after a long illness,” on Twitter. A writer of immense range and output, capable of 6,000 words a day when in harness, Mr. Johnson modeled his career after earlier English men of letters, like Thomas Babington Macaulay and G.K. Chesterton. With an affable prose style and supreme...