A member of the Adventist Church, Blackmer was a composer and songwriter. He attended the Wilbraham Academy, but when it came to music, he was largely self taught. He wrote his first song at age 16, and went to write over 300 more during his life. He lived mostly in Somerville, Massachusetts, near Boston, and had a pianoforte business. He directed the choir at the Advent Christian Church in Somerville, and was a song leader at the Alton Bay camp meetings in Lake Winnepesaukee, New Hampshire (1914-1930).