After receiving a thorough English education, Gaines studied law, was admitted to the bar and began practice in his hometown of Walton.
Gaines served as a common soldier in the War of 1812, fighting in the battle of the Thames. When the Mexican War broke out he was commissioned major-general in Thomas Marshall’s Kentucky cavalry brigade and distinguished himself in the battle of Molino del Rey.
In January 1847, he was captured by the Mexicans at Incarnation and detained some months in a military prison, from which he escaped. He then served as aide-de-camp on the staff of Gen. Winfield Scott.
His record in Congress is not significant. President Taylor appointed him governor of Oregon Territory after Abraham Lincoln declined that office. Gaines accepted, shipped with his family on the store ship Supply around the Horn, and arrived in San Francisco in July 1850.
From San Francisco the Gaines family proceeded to Oregon on the ship-of-war Falmouth, arriving August 15.
In 1853, his term of office expired. He settled on a farm near Salem, where he spent the remainder of his life.
During his imprisonment in Mexico, Gaines was elected as a Whig from his district to the Thirtieth Congress (1847 - 49).
Gaines was received with much ceremony, but there was opposition to federal officers appointed from outside the Territory and there was also a tendency toward Democracy in politics which made his stiff Whiggism distinctly unpopular.
Gaines was under the influence of bad political advisers. While personally honorable, and devoted to the public welfare, he had the misfortune within a few months to see the people of the Territory factionalized, the legislature and the supreme court disrupted, and the interests of the community he had been sent to serve generally disturbed and jeopardized.
The principal occasion of difficulty was the question of relocating the capital of the Territory, Oregon City and Salem being rivals for the honor. Those who urged the retention of Oregon City as the seat of government as well as the so-called “Salem Clique, ” were to some extent animated by speculative interest.
The latter, through their organ the Oregon Statesman, edited by Asahel Bush, abused Gaines viciously. “Breakspeare” makes Bush say of him, keeping close to the language of his vitriolic sheet: By way of retaliation Gaines assaulted Bush on the street in Salem and so the unseemly quarrel raged month after month.
Technically, Gaines was at least half right. A majority of both houses of the legislature had voted to fix the permanent capital at Salem. Gaines favored Oregon City and, being in control of the funds appropriated by Congress for public buildings, he was able to checkmate the Salem party.
He argued that the law locating the capital was unconstitutional because the enabling act had provided that no law could cover more than one subject, whereas the act in question not only fixed the capital at Salem and gave the penitentiary to Portland and the university to Marysville, but also provided for endowing the university.
The opposition did not feel confident that their law would be held constitutional, and it was in fact pronounced null and void by the United States attorney-general, but, in any event, Congress would have to approve all territorial acts before they became operative. Congress eventually gave its approval to this and other laws passed by the majority of the legislature sitting at Salem, thus lowering Gaines’s prestige.
Gaines had been a member for several terms of the Kentucky legislature.
Gaines was a man of distinguished appearance, with great personal dignity, more than a touch of pompousness, and a rather marked deficiency of humor.
On June 22, 1819, Gaines married Elizabeth, daughter of Nicholas Kincaid of Versailles, Kentucky.
On the voyage to San Francisco in July 1850, two of his daughters, beautiful and accomplished young women died of yellow fever.
His wife was killed by accident in the fall of 1851, and a son Richard died soon afterward.
About fifteen months after his wife’s death, Gaines married Margaret B. Wands, one of the five women teachers sent to Oregon by Gov. Slade.