In 1859, Greene formed a law partnership with Cyrus Bently in Chicago, Illinois. He practiced law and lived there for five years. In the winter of 1864 he moved to McGregor, Iowa and helped his brothers build the McGregor Western Railroad. During this time, and several years later, he helped build the Rockford, Rock Island & St. Louis Railroad. He returned to Cedar Rapids after this, and began practicing law with Judge Dudley and his son-in-law A. S. Belt. The firm represented the Chicago & Northwestern Railroad. Greene continued to be involved with railroads, and became president of the Burlington, Cedar Rapids & Minnesota Railroad, which he took an active part in building. When the railroad went bankrupt it was purchased and operated under the name Burlington, Cedar Rapids & Northern Railroad. He constructed several smaller railroads in Iowa, Illinois, Minnesota, Missouri, and Kansas.