His entry into politics came in 1837 with his appointment by
Martin Van Buren as Collector of Customs of the Port of Boston. In 1844, he was the Republican candidate for the governorship of Massachusetts, but he was defeated. In 1845, in recognition for his support at the previous Democratic convention, he entered
Polk's cabinet as
Secretary of the Navy, serving until 1846, when for a month he was acting
Secretary of War. During this short period in the cabinet he established the
United States Naval Academy at
Annapolis, gave the orders which led to the occupation of
California, and sent
Zachary Taylor into the contested land between
Texas and
Mexico. He also continued his pleadings for the annexation of Texas, as extending "the area of freedom," and as a democrate, took high moral ground as to the propriety of slavery.
He likewise made himself the authority on the
Oregon boundary dispute, with the result that in
1846 he was sent as Minister Plenipotentiary to
London, where he lived in constant companionship with the historian
Macaulay and the poet
Hallam. With the election of
Zachary Taylor his post was not renewed; on his return to the United states in 1849 he withdrew from public life, residing in
New York and writing history.
In April of 1864, at Bancroft's request,
President Lincoln wrote out what would become the fourth of five known manuscripts of the
Gettysburg Address. Mr. Bancroft planned to include this copy in "Autograph Leaves of Our Country's Authors," which he planned to sell at a Soldiers' and Sailors' Sanitary Fair in Baltimore.
In 1866, Bancroft was chosen by Congress to deliver the special eulogy on Lincoln; and in 1867 he was appointed minister to
Berlin, where he remained until his resignation in 1874. Then he lived in
Washington, D.C., summering at
Rose Cliff, Newport, Rhode Island.
His latest official achievements are considered the greatest. In the San Juan arbitration he displayed great versatility and skill, winning his case before the emperor with brilliant ease. The naturalization treaties, named the "
Bancroft treaties" in his honor, which he negotiated successively with
Prussia and the other north German states were the first international recognition of the right of
expatriation, a principle since incorporated in the law of nations.
Several ships have been named
USS Bancroft for him. Bancroft was the last surviving member of the Polk cabinet.