Educated at Bowdoin College, Andrew was a radical abolitionist of slavery from an early age, engaged in the legal defense of fugitive slaves against owners seeking their return.

He provided legal support to John Brown after his 1859 raid on Harpers Ferry, Virginia, raising his profile and propelling him to the Massachusetts governor's chair.

His father, Jonathan Andrew, was descended from an early settler of Boxford, Massachusetts, and ran a small but prosperous merchant business in Windham.

[10] Andrew participated in the establishment in 1848 of the Free Soil Party, whose principal political goal was ending the expansion of slavery into western territories.

[21] Anger over that year's passage of the Kansas-Nebraska Act (which overturned the limitation of slavery's expansion under the Missouri Compromise of 1820) revitalized the Free Soil movement.

Andrew led the debate in favor of removing Judge Edward Loring from office over his actions in the Burns case, and in opposition to the proposed repeal of the state's stringent anti-slavery personal liberty law.

[29] In anticipation of gaining a higher elected office, Andrew refused Governor Banks' offer of a seat on the Superior Court bench in 1859.

[31] Andrew's efforts on behalf of Brown brought him statewide notice, and also drew the attention of Southern interests in the United States Senate.

Banks sought to put off the announcement of his retirement until the last possible moment, but state Republican chairman William Claflin leaked the news to Andrew supporters.

[36] Andrew won the nomination by a wide margin, and defeated Constitutional Union Party candidate Amos A. Lawrence in the general election.

[37] When Andrew took office on January 2, 1861, on the eve of the American Civil War, the Albany Argus called him "a lawyer of a low type and a brutal fanatic" who "proposes to maintain the condemned [personal liberty] statutes of [Massachusetts], and to force upon the South by arms, an allegiance to the Constitution thus violated.

[39] Shortly after taking office, Andrew began to ready the Massachusetts militia for duty, promoting younger and more vigorous leaders, and contracting for updated armaments, equipment, and supplies.

[42] With the war already underway in late 1861, Andrew engaged in a highly public dispute with General Benjamin Franklin Butler, who sought to appoint officers of regiments he recruited.

Andrew ended up winning in the disagreement, and (in a response viewed at the time as somewhat petulant) refused to appoint any of Butler's choices to those positions.

When Lincoln announced his preliminary Emancipation Proclamation in September 1862 (shortly after the Union victory in the Battle of Antietam), Andrew was supportive, but called it "a poor document but a mighty act", and complained that it was too limited in scope and late in becoming effective.

[45] Andrew was a leading force in promoting the enlistment of black men as uniformed soldiers in the Union Army, although the state legislature was at first reluctant to authorize it.

[46] Abolitionist Frederick Douglass had advocated this from the start of the war, and Andrew viewed it as a necessary equalizing step, and a means to fill the state's enlistment quotas with something other than factory workers.

In late 1865, he expressed support for the Reconstruction policies of President Andrew Johnson, resulting in a split with his longtime political ally Charles Sumner.

[53] He had in part acted on private efforts to aid in the reconstruction of the south in 1865, forming a land agency as a clearing house for Northerners seeking to invest in the southern properties.

[54] Andrew was elected a 3rd Class Companion (honorary member) of the Pennsylvania Commandery of the Military Order of the Loyal Legion of the United States in recognition of his support of the Union during the Civil War.

In 1861, both outgoing Governor Banks, and Andrew, after he took office, refused to sign a bill authorizing additional funding to the financially troubled project.

[60] In support of the war effort, he rescinded a ban, enacted by the Know Nothing Governor Henry J. Gardner, against the formation of militia companies composed of immigrants.

[61] On July 14, 1863, in response to a draft riot that broke out among Irish Catholics in the North End of Boston, Andrew ordered six companies and additional regular troops to protect Union armories in the neighborhood from attempts by the rioters to raid them.

When President Johnson engaged in political attacks against Charles Sumner in 1866, charging him with treason, Andrew decided to withdraw from the contest.