Blackmar was a merchant and farmer in partnership with his brother, and their endeavors included buying and selling grain and produce, boat building, and
shipping grain and other commodities on the
Erie Canal. He was active in the
New York Militia, serving as Quartermaster of the 5th Horse Artillery Regiment, and later holding the position of regimental
Lieutenant Colonel and second-in-command. From 1834 to 1835 Blackmar served as Newark's
Town Supervisor. Blackmar was a member of the
New York State Assembly (Wayne County) in
1838 and
1841. His business expanded to include shipping produce to
Michigan,
Iowa and
Illinois. In 1844 he donated the land for the original campus of
Hillsdale College in Michigan. He also served as Treasurer and a member of the board of directors of the
Sodus Point and Southern Railroad. Elected as a
Whig to the
30th United States Congress to fill the vacancy caused by the death of
John M. Holley, Blackmar held the office of United States Representative for the 27th district of New York from December 4, 1848, to March 4, 1849. Afterwards he resumed his former business activities in Newark. Blackmar served again as Town Supervisor from 1852 to 1853. ==Death==