Seager came to Canada from England about 1832. He traveled and sketched in Panama and Cuba in the 1830s. He was living on Tremont Road in Boston in 1838. He made his first trip to the White Mountains in 1839. In 1844 he became drawing master at the English High School in Boston where the sculptor John Rogers was one of his students. He became the first professor of drawing and drafting at the United States Naval Academy, Annapolis, from 1850 to 1867. He lived in Baltimore, MD in 1871.
He made sketching trips to New Hampshire in 1861, 1863, and during the 1870s.
He exhibited at the Boston Athenaeum in 1847 and 1848.
Titles of his New Hampshire paintings include Mount Washington, New Hampshire; Notch of the White Mountains, NH; Sandwich Hills, Squam Lake, New Hampshire; and Waterfall in the Franconia Notch, NH.