John William Thomas (January 4, 1874 – November 10, 1945) was an American politician, a United States Senator from Idaho.

A Republican, he served for a total of over ten years in two different seats, both times appointed after his predecessor died in office.

Born on a farm in northern Kansas near Prairie View in Phillips County, Thomas attended the rural schools and the Central Normal College at Great Bend.

He was appointed to the U.S. Senate for the first time in 1928 to fill the vacancy caused by the death of his political mentor, Frank Gooding, by Governor H. C.

1933), served for over two decades in the Idaho state senate, switching parties in 1978, and was the Democratic nominee for lieutenant governor in 1994.