Joseph was educated at Reverend Enoch Green’s school in Deerfield Township, New Jersey, where Enoch was the pastor of the local Presbyterian Church. Bloomfield studied law, was admitted to the bar in 1775 and began his law practice in Bridgeton, New Jersey. He entered the Continental Army as captain of the 3rd New Jersey Regiment on February 9, 1776. He attained the rank of major on November 28, 1776, and was appointed judge advocate of the northern army. He was wounded at the Battle of Brandywine in September 1777. He resigned from the Continental Army on October 28, 1778, after he was elected clerk of the New Jersey General Assembly.