Herman H. Halladay was born January 4, 1869 in Clinton Township, Lenawee County, Michigan to Addison P. and Henrietta Rosetta Halladay. After graduating from Clinton High School, he attended Adrian College and was a schoolteacher. On April 5, 1893, he was married to (Sarah) Virginia Daniels (September 1870 – August 2, 1961). Together they had two daughters, Hope Hermina Flynn (November 13, 1901 – September 13, 1987) and Louise Virginia Carpenter (September 21, 1895 – June 29, 1983).

Halladay was appointed state livestock commissioner by Governor Chase Osborn in 1912. After serving in that position for six years, he was appointed commissioner of the Bureau of Animal Industry by Governor Albert E. Sleeper. Halladay was among the first to suggest creating a State Park at Wampler's Lake in the heart of the Irish Hills. In 1920, the site became one of the first 25 state parks in Michigan. It was renamed W. J. Hayes State Park in 1930.

In December 1921, Halladay became the Secretary of the State Board of Agriculture (now known as the Board of Trustees), Michigan State College’s governing body. He retired from Michigan State College (now called Michigan State University) in January 1935. According to his obituary, Halladay was an early member of the Lansing Rotary Club and served in many civic posts. Halladay died on September 10, 1943, in Ann Arbor, Michigan.