After gaining recognition as one of the most prominent members of the Suffolk bar, he became associated in 1848 with the Free Soil movement, and took a prominent part in the Buffalo convention of that year.
In politics Field was originally an anti-slavery Democrat, and he supported Van Buren in the Free Soil campaign of 1848.
He served from 1852 to 1856 in the Missouri legislature as a Free Soil Democrat, in 1856 joined the Republican party, and in1857-1859and1861-1862was a member of Congress, where he proved an able debater.
In 1848 he left the Whig party and became one of the chief leaders of the Free Soil party, serving as presiding officer of that party's national convention in 1852, acting as chairman of the Free Soil national committee and editing from 1848 to 1851 the Boston Republican, which he made the chief Free Soil organ.
He was a Free Soil candidate for Congress (1850), but was defeated; was indicted with Wendell Phillips and Theodore Parker for participation in the attempt to release the fugitive slave, Anthony Burns, in Boston (18J3); was engaged in the effort to make Kansas a free state after the passage of the Kansas-Nebraska Bill of 1854; and during the Civil War was captain in the 51st Massachusetts Volunteers, and from November 1862 to October 1864, when he was retired because of a wound received in the preceding August, was colonel of the First South Carolina Volunteers, the first regiment recruited from former slaves for the Federal service.
An enthusiastic humanitarian on all subjects, Dr Howe was an ardent abolitionist and a member of the Free Soil party, and had played a leading part at Boston in the movements which culminated in the Civil War.
He was ardently opposed to the extension of slavery and supported Martin Van Buren, the Free Soil candidate for the presidency in 1848.
In 1854 the newly organized Republican party, formed largely from the remnants of the Whig party and including most of the Free Soil Democrats, with the aid of the temperance issue elected Myron Holley Clark (1806-1892) governor.