John Davis was born on 13 January 1787 in Northborough, Massachusetts, to Deacon Isaac Davis and Anna Brigham Davis. He received his early schooling locally before attending Leicester Academy and then Yale College, from which he graduated in 1812. Following graduation, he studied law in Worcester under the attorney Francis Blake, gaining admission to the Massachusetts bar three years later. His first independent practice was in Spencer, but he soon returned to Worcester, eventually taking over Blake's own practice. He was also briefly in partnership with Levi Lincoln Jr., a relationship that dissolved when Lincoln was appointed to the Massachusetts Supreme Judicial Court in 1824. In 1821, Davis was elected to the American Antiquarian Society, an early sign of his standing in the region's civic and intellectual life.
Davis entered politics in 1824, winning election to the United States Congress. He would go on to represent Massachusetts in the House of Representatives for a decade, serving through the 19th, 20th, 21st, 22nd, and 23rd Congresses from 1825 to 1833. During these years he was a committed supporter of John Quincy Adams, backing Adams's successful presidential campaign and consistently favoring the conservative fiscal policies that Adams championed. Davis aligned himself firmly with the National Republicans and, later, with the emerging Whig Party. In a state whose economy was becoming increasingly defined by textile manufacturing and industrial growth, he championed protectionist tariff legislation with conviction. His speeches supporting the Tariff of 1828 were widely reprinted, establishing his reputation as a serious advocate for the industrial interests of Massachusetts. He opposed the policies of Andrew Jackson and aligned himself with Henry Clay, though he drew the line at Clay's proposed compromise tariff of 1833, which he considered inadequate.
In 1833, National Republican Party leaders urged Davis to run for Governor of Massachusetts in what became a three-way contest. His opponents were the former President John Quincy Adams, running on the Anti-Masonic ticket, and Democrat Marcus Morton. Davis drew his political support from textile interests and a faction of the National Republicans led by Abbott Lawrence, as well as from the outgoing Governor Levi Lincoln Jr. The result was a plurality for Davis but not the majority then required to win outright, which sent the decision to the state legislature. When Adams withdrew, the Whig-controlled legislature chose Davis over Morton, giving him the governorship. The Whig majority declined to reward the Anti-Masons for Adams's cooperative gesture, foreclosing any prospect of the two parties working together going forward.
Davis was reelected governor in 1834, aided in part by public hostility in Massachusetts toward President Jackson's assault on the Second Bank of the United States. His two terms in the corner office were not distinguished by bold legislative initiatives. He largely continued the business-friendly fiscal and economic policies of his predecessor Levi Lincoln Jr., presiding over a period in which the state's transportation infrastructure expanded steadily and its industrial base continued to grow. He was known above all for his personal rectitude, a quality that earned him the nickname Honest John Davis and set him apart from many contemporaries in an era when political corruption was widely understood to be endemic.
After his two terms as governor, Davis moved to the United States Senate, where he served most of one term before resigning in 1841 to accept election as governor again. His second governorship was regarded as unremarkable, and his relationship with fellow Whig Daniel Webster deteriorated over a series of disagreements. In 1843 he lost the gubernatorial election to the Democrat Marcus Morton, the same opponent he had beaten a decade earlier. He was returned to the Senate in 1845 and served until 1851.
The defining political cause of Davis's Senate career was his opposition to the expansion of slavery. He opposed the Mexican-American War and worked consistently to prevent slavery from extending into the territories acquired through conflict. He was not, however, a hard-liner on the question: he voted for most of the provisions of the Compromise of 1850, a position that reflected his characteristic preference for institutional accommodation over confrontation. He retired from public life in 1853 after twenty-five years of continuous service, having moved through both houses of Congress and the statehouse without ever becoming a figure of historical drama. He died on 19 April 1854, leaving behind a reputation for integrity that outlasted the particular causes he had championed.
