Jenkins was admitted to the bar that same year (1907) and commenced practice in Ironton, Ohio.

In 1923 and 1924, Jenkins served in the Ohio Senate and was a delegate to the Republican State convention in 1920 and 1924.

After the Dunkirk evacuation and during the Battle of Britain Jenkins spoke out in favor of giving aid to the British and campaigned against isolationism.

He had a reputation for being so outspokenly pro-British that in the 1940 election, his opponent, isolationist Democrat John P. Kelso referred to him as the "Congressman from London."

Jenkins responded by calling his opponent a "Craven stooge for Herr Hitler."