Born in Dolphsburg, New York on October 19 1835, Dolph attended Genesee Wesleyan Seminary, studied law, and was admitted to the bar in 1861. He set up practice in Schuyler County, New York. In 1862 he enlisted in the Oregon Escort, which protected settlers traveling to Oregon from Native Americans.
He settled in Portland, Oregon, becoming the city's attorney from 1864 to 1865 and a United States district attorney from 1865 to 1868. He was elected to the Oregon State Senate in 1866, 1868, 1872, and 1874. In 1882 he was elected to the United States Senate and reelected in 1888. He gave a speech in McMinnville, Oregon, at McMinnville College (now Linfield College) on May 31 1882 at the laying of the cornerstone for the first building on campus, which is known today as Pioneer Hall. He became the chairman of the United States Senate Committee on Coast Defenses in the Forty-ninth through Fifty-second Congresses and the United States Senate Committee on Public Lands in the Fifty-second Congress. In total he served from March 4, 1883 to March 3, 1895, being an unsuccessful candidate for reelection in 1894. He moved back to Portland where he died on March 10, 1897. Dolph was interred there in River View Cemetery.