In 1908 he inherited a small country house, Plas Brondanw, from his father, restoring and embellishing it over the rest of his life, and rebuilding it after a fire in 1951. He served with distinction in the First World War, serving first with the Royal Fusiliers and then the Welsh Guards attached to the Tank Corps, with whom he was awarded the Military Cross in the 1918 New Year Honours.

In 1915 Williams-Ellis married the writer Amabel Strachey. Their son, Christopher Moelwyn Strachey Williams-Ellis (1923–13 March 1944), a Lieutenant in the Welsh Guards, was killed in action in Italy during the Second World War and was buried in plot VIII, row C, grave 24 at Minturno War Cemetery. Their elder daughter, Susan Williams-Ellis (1918-2007), used the name Portmeirion Pottery for the company she created with her husband in 1961. The second daughter, Charlotte Rachel Anwyl Williams-Ellis (1919-2010), was a zoologist and environmentalist with a Cambridge Ph.D. in agricultural science. She married the agriculturalist Lindsay Russell Wallace in 1945, and moved to New Zealand.

In 1929 Williams-Ellis bought portrait painter George Romney’s house in Hampstead.

In 1958 Williams-Ellis was made a Commander of the Order of the British Empire “for public services”. He was made a Knight Bachelor in the New Years Honours List of 1972 “for services to the preservation of the environment and to architecture”. At the time, he was the oldest person ever to be knighted.

Sir Clough Williams-Ellis died in April 1978, aged 94. In accordance with his wishes, he was cremated, and his ashes went to make up a marine rocket, which was part of a New Year’s Eve firework display over the estuary at Portmeirion some twenty years after his death.