Born in Trenton, N. J., Daniel Agnew grew up in Pittsburgh, graduated from the Western University of Pennsylvania in 1825, was admitted to the bar when only 18, and began to practice law in Beaver in 1829. He was a delegate to the state Constitutional Convention in 1837, in 1851 was appointed President Judge of the l7th District (Beaver, Butler, Lawrence and Mercer counties) and was elected to the same office in 1861. An ardent Unionist he was elected to the state supreme court in 1863, and named chief justice in 1873. "Seeking the truth with conscientious industry, no cause was too small to merit his thorough investigation, none too large for the comprehensive grasp of his powers." After his retirement from the bench in 1879, except for two important legal cases, he devoted his life to writing articles on the law and local history, and received honorary degrees from Washington College and from Dickinson University.