He served as physician with the Real del Monte Company in Mexico, during which period he collected plants in the region. He is best remembered for exploration and botanical research in Mexico, Arizona and Alta California in the early 19th century. He subsequently returned to Ireland in 1834 and became curator of the herbarium at Trinity College, Dublin.
E. Charles Nelson & Alan Probert. A Man Who Can Speak Of Plants / Dr Thomas Coulter of Dundalk in Ireland, Mexico and Alta California. Privately published by E. Charles Nelson, Dublin, 1994. ISBN 0-9524847-0-6