Professor Philip James Stradling Williams (11 January 1939 – 10 June 2003) was a Welsh politician for Plaid Cymru and scientist.

He was educated at Lewis School, Pengam and Clare College, Cambridge,[1] and became a leading space scientist.

He was appointed Professor of Solar Terrestrial Physics at the University College of Wales, Aberystwyth, and simultaneously became economic spokesman for Plaid Cymru.

He contested the 1968 Caerphilly by-election, where he came close to unseating Labour in a safe seat, and became the second Chairman of Plaid Cymru in 1970, a post he held until 1976; when he became vice president of the party.

Williams also stood for election in Blaenau Gwent in 1999 and got 21% of the vote.