During his work in public service, Benjamin worked on his law degree from Valparaiso University, he graduated with his Juris Doctor and was admitted to the Indiana Bar Association in 1966. Shortly after Benjamin was admitted to the Indiana Bar, he ran for a seat in the Indiana House of Representatives, winning two consecutive terms in 1966, and in 1968. Benjamin served in the Indiana House until he won a seat in the Indiana Senate in 1970, winning reelection in 1974, and served in the Indiana Senate from 1971 to 1977. During his time in the Indiana Senate, Benjamin was named Outstanding State Senator by newsmen assigned to report on the Indiana General Assembly. As a state legislator, Mr. Benjamin developed a new code of ethics for legislators, worked on a new state medical malpractice act, and facilitated court reform for the Lake County Superior Court system. Two years after Benjamin won a seat in the Indiana Senate, he challenged incumbent 12-term Congressman Ray J. Madden for the Democratic nomination for Indiana's 1st congressional district, but eventually lost the hotly contested primary. By 1976, having gained significant name recognition as an Indiana legislator, Benjamin again challenged Madden in the Democratic primary, this time defeating him with 56% of the vote, compared with Madden's 34%. In the general election Benjamin beat evangelical Protestant educator, and co-founder of Moral Majority, Robert J. Billings, with a 40% margin of victory.