He came to the United States in 1820 with his parents, and they settled in Watertown, New York. He attended Union Academy at Belleville, and graduated from Union College in 1833. Then he taught school and was Principal of Union Academy, and subsequently taught at Watertown Academy. Then he studied law, and was admitted to the bar in 1837. In January 1839, he married Lydia Maria Ten Eyck, a daughter of Egbert Ten Eyck.
Mullin was District Attorney of Jefferson County from 1843 to 1845. He was elected as a Whig to the 30th United States Congress, holding office from March 4, 1847, to March 3, 1849. He was President of the Village of Watertown in 1853 and 1854.
He was buried at the Brookside Cemetery, in Watertown.
State Senator Joseph Mullin (1848–1897) was his son.
- United States Congress. "Joseph Mullin (id: M001072)". Biographical Directory of the United States Congress.
- The New York Civil List compiled by Franklin Benjamin Hough (pages 351 and 375; Weed, Parsons and Co., 1858)
-  Court of Appeals judges
|United States House of Representatives|
|Member of the U.S. House of Representatives
from New York's 19th congressional district
Charles E. Clarke