William Kavanaugh Oldham was born in Richmond, Kentucky. Oldham was educated at Central University in Richmond.
Oldham moved to Pettus in Lonoke County, Arkansas in 1885.
He was elected to the Arkansas House of Representatives in 1907. He served as a member of the Senate from 1911 to 1913. Oldham was selected as president of the Senate in 1913.
When Governor Joseph Taylor Robinson resigned from office on 10 March 1913 Oldham became Governor of Arkansas. Oldham served for six days and turned his office over to the newly elected president of the Senate Junius Marion Futrell.
Oldham retired from public service and returned to farming.
William K. Oldham died in Pettus, Arkansas and is buried at the Oaklawn Cemetery in Little Rock, Arkansas.