William Clarke was born at Kerikeri in 1827, the fourth child, and his middle name was originally Yate — given for the missionary William Yate, who had been a beloved presence in the Clarke household. George Senior had that name struck from the register in 1835 after Yate was disgraced by scandal.
William married Mary Anne Kemp at Waimate on 28 April 1852 — the same joint ceremony as his brother Henry. The two Clarke brothers and their two Kemp wives all moved into Prospect, the family's Waimate North property. William and Mary farmed Prospect for decades. William retired in 1880, transferring the property to his son William Junior, and moved to "Resthaven" on Clonbern Road in Auckland. He died on 26 August 1914 — a span of eighty-seven years that reached from the mission world at Kerikeri to the beginning of the First World War.
William and Mary had six children: Annie, Alice, William, Emily, George, and Frederick.