He was born in Greenfield, Massachusetts on December 25, 1786, to parents George and Lydia (Stevens) Grennell.
He was admitted to the bar in 1811 and served as prosecuting attorney for Franklin County 1820–1828.
Grennell served as a trustee of Amherst College 1838–1859, a judge of probate 1849–1853, clerk of Franklin County Courts 1853–1865, and the first president of the Troy and Greenfield Railroad.
Grennell married twice: first to Helen Adelle Blake in 1814 and second to Eliza Seymour Perkins in 1820.
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