Born on January 4, 1847 in Albany, New York to Andrew James Colvin, a wealthy lawyer, and his second wife, Margaret Crane Alling; his first name was his grandmother's maiden name. He was tutored for several years before entering The Albany Academy; then, during the Civil War the family moved to Nassau; there he attended Nassau Academy, where he excelled in the sciences, and graduated in 1864. Although he preferred attending West Point Military Academy, he joined his father's law office in Albany and was later admitted to the bar. Working in real estate law gave him his first experience in surveying.
In 1865, when Colvin was 18, Alfred Billings Street gave him a copy of his 1860 book, Woods and Waters, about his adventures in the Adirondack Mountains. The next three years, Colvin spent his summers exploring the Adirondack wilderness. By 1869, he had formed the idea of doing a geological survey of the Adirondack region. To gain experience, he recruited friend Mills Blake for a trip to nearby the Helderberg Mountain; he wrote an illustrated report of the trip that was published in Harpers New Monthly Magazine, a national publication.
During the summer of 1869 he climbed Mount Marcy, and in 1870 made the first recorded ascent of Seward Mountain. During the ascent of Seward, Colvin saw the extensive damage being done by lumbermen in the Adirondacks. His report of the climb was read at the Albany Institute, where it garnered the attention of state officials, and was printed in the annual report of the New York State Museum of Natural History. In it, he tied clear-cutting of Adirondack forests to reduced water flow in the state's canals and rivers, an idea that had first appeared in George Perkins Marsh's Man and Nature, published in 1864.
In 1872 he applied to New York for a stipend to cover the costs of a survey; he was subsequently named to the newly created post of Superintendent of the Adirondack Survey and given a $1000 budget by the state legislature to institute a survey of the Adirondacks. He was an able administrator, managing crews of up to 100 men separated by difficult terrain with only primitive communication methods. He also designed and built some tools for the job, including a folding canvas boat, and a wind powered spinning reflector to enable precise sighting of a mountain top from many miles away.
During the first year he discovered Lake Tear-of-the-Clouds, often considered the source of the Hudson River. He directed surveying parties throughout the Adirondacks and determined the altitudes of most of the highest peaks, becoming obsessed with his task. Determined to fix the precise altitude of Mount Marcy (having decided that the barometric method of determining altitude was insufficiently accurate) he ran a series of eight hundred chains and levels over forty miles long from Lake Champlain to Marcy, each intermediate altitude being calculated to one thousandth of an inch. As the crew approached the summit of Marcy, they encountered an October snow storm with ice and freezing rain; despite urging by his guides and assistants to wait for better weather, Colvin pushed on despite the danger of becoming trapped in Panther Gorge.
In 1873 he wrote a report arguing that if the Adirondack watershed was allowed to deteriorate, it would threaten the viability of the Erie Canal, which was then vital to New York's economy, and that the entire Adirondack region should therefore be protected by the creation of a state forest preserve. He was subsequently appointed superintendent of the New York state land survey, which led to the creation of the Adirondack Forest Preserve in 1885. His work ended in 1900 when then Governor Theodore Roosevelt transferred his duties to the state engineer.
He was a member of numerous scientific societies and was president of the department of physical science at the Albany Institute. About 1881, at Hamilton College, he delivered lectures on geodesy, surveying, and topographical engineering. His maps, reports, illustrations and notes form a large part of the archives of the New York State Department of Environmental Conservation in Albany and are often referred to by present-day surveyors. In 1891, he ran on the Republican ticket for New York State Engineer and Surveyor but was defeated by Democrat Martin Schenck.