Sawyer was born in Montgomery County, Ohio. In 1818 he began to learn the trade of blacksmithing. He worked at this occupation in both Dayton, Ohio, and Grand Rapids, Michigan. In 1829 he settled in Miamisburg, Ohio. From 1832 to 1835 Sawyer served in the Ohio House of Representatives, filling the position of speaker in 1835. In 1838 and 1840 he ran unsuccessfully for congress.

In 1843 Sawyer moved to St. Marys, Ohio. He was elected to United States Congress as a Democrat in 1844. He was reelected in 1846 but did not run for re-election in 1848.

Sawyer 'liked to stand by the Speaker's chair during debates noisily munching sausages and cornbread and using his pants for a napkin and his jack-knife for a toothpick'.^[1]

In 1850-1851 Sawyer served as a member of the Ohio State Constitutional Convention. He served another term in the State House in 1856. He also served as mayor of St. Marys and a Federal land agent in Minnesota.

[Sawyer] would never submit to the slave States sending their emancipated blacks within her borders or colonies. He...said, if the test must come, the banks of the Ohio (a mile wide) would be lined with men with muskets on their shoulders to keep off the emancipated slaves which the slave States might attempt to throw in among them.

— Narration of William Sawyer's speech in United States House of Representatives, June 22, 1848, source

• Congressional biography