Leslie graduated from the Indiana Law School in 1907. He opened a law office in Lafayette the year he graduated and took a position at a local high school coaching football. There he met Martha Morgan, whom he married on August 16, 1910, and by whom he had three sons, Jack, Richard, and Robert. Leslie became involved in local politics and was elected as a Republican Tippecanoe County treasurer in 1912. He purchased a farm in 1914, but disliking the labor, he sold the farm and bought stock in a local bank at which he served as president until 1924.