A native of Sewickley Township, Pennsylvania, Cowan worked as a carpenter, boatman, and teacher before graduating from Franklin College in New Athens, Ohio, in 1839.

Cowan also became active in politics as a Whig, and campaigned for the party's presidential candidates beginning with William Henry Harrison in 1840.

[2] After attending the academy in Greensburg, Pennsylvania, Cowan returned to teaching school briefly before enrolling at Franklin College in New Athens, Ohio.

[2] After his college graduation, Cowan studied law with Henry Donnel Foster, was admitted to the bar and commenced practice in 1842.

In the election by the full legislature, Cowan defeated his former law teacher Henry Donnel Foster by a party-line vote of 98 to 38.

Anxious not to make an enemy of the head of the Republican Party in such an important state, Lincoln eventually made good on the commitment to Cameron by appointing him as Secretary of War.

[3] Concerned that the bridge would limit the ability of boats and ships to transport cargo on the river, and opposed to what he saw as the expanding power of the Pennsylvania Railroad, Cowan supported revising the initial proposal, which resulted in lengthening the span to 300 feet and raising the deck to 90 feet above water level, which ensured that steamboat smokestacks would be able to clear it.

With respect to the Union effort during the American Civil War, Cowan received credit for authoring the proposal to allow individuals drafted for military service to be excused from serving after paying a $300 commutation fee.

[3] The commutation fee was intended to keep the cost of hiring a substitute (another route available to draftees wishing to avoid service) from becoming excessive.

Despite the stated intent for enacting the commutation fee, it was one of the most hated policies of the war, with members of the poor and working classes protesting that it allowed the wealthy to avoid military service at their expense.

"[6] While largely invoking gender and marriage to make his points about states' rights, his arguments helped create a legal distinction between sex and race in federal law.

In the senate, while trying to elucidate the meaning of the Thirteen Amendment, he stated, "What was the involuntary servitude mentioned there.... Was it the right the husband had to the service of his wife?

In response to arguments by the likes of Senator Cowan, the Civil Rights Act of 1866 was written to only apply to "race" and "color," but did not include gender.

[7] Cowan was a candidate for reelection with the support of Democrats in the Pennsylvania legislature, but lost to former ally Simon Cameron.