After graduation, Roosevelt enrolled in the Boston University School of Law. He also took a sales job with the firm of Victor De Gerard of Boston in 1930, remaining with that firm when it amalgamated with the John Paulding Meade Company which, in turn, amalgamated with O'Brion, Russell and Company in 1932. Roosevelt was so successful, that within one year, he had abandoned his law studies. In 1932 he started his own insurance agency, Roosevelt & Sargent, in partnership with John A. Sargent. As president of Roosevelt & Sargent, he made a substantial fortune (about $500,000, or more than $9 million in 2018 dollars). He resigned from the firm in 1937, when he officially went to work in the White House, but retained his half ownership. He was also elected a director of Boston Metropolitan Buildings, Inc. in 1933. Roosevelt also served briefly as president of the National Grain Yeast Corporation from May to November 1935.
His first marriage was in 1930 to philanthropist Betsey Maria Cushing (1909–1998), the middle daughter of surgeon Harvey Williams Cushing and Katharine Stone Crowell. James and Betsey had two daughters, Sara (b. 1932) and Kate (b. 1936), before divorcing in 1940.