His hopes of entering the diplomatic corps were thwarted after the death of his father and he started an importing business instead. He spent the next few years traveling the world buying rugs and antiques before getting married and settling down. His travels were extensive and included Europe, Russia,the Near East, North Africa (9 weeks with own caravan), the West Indies, Central Africa, and a ride across Central America on horseback. He lived in New York City and was in a famous Cavalry division of the National Guard and played quite a bit of polo. This set the tone for him as he continued to travel and indulge his interest in hunting the rest of his life.
By 1927 he was getting ready to settle down and get married when a chance meeting with one of his college professors, John Gallishaw, encouraged him to take a stab at writing. He took Gallishaw's course in short fiction on the condition that he pay for the course out of future sales. He married socialite Dorothy L. MacReady in New York City in November of that year and by May 1928 he had his first story published. He enjoyed immediate success selling to the pulp magazines and sold 18 stories before his first rejection. The magazines paid well at that time and he was soon able to build a comfortable home outside of Baltimore, Maryland. In 1930 he published his first book The Seeds of Murder which introduced Captain Hugh North, a detective in Army Intelligence and the hero in a long series of "intrigue" novels.
By 1931 he had settled into a career as an author of books as well as short fiction, publishing two more Captain North novels and his first historical novel, Captain Nemesis, which was republished from an earlier pulp serial. The historical novel apparently did not sell well because he went back to the mystery/intrigue books, publishing a dozen or so over then next 7 years. He developed his Hugh North character, who was Mason's alter ego, in these books. North was a prototype for James Bond in that he was a smooth, capable spy, as well as quite a lady killer. This series of books also seemed to predict actual military events before they took place, including a sneak attack on Pearl Harbor.
Mason was still selling historical stories for the pulps during this period and in 1938 returned to the genre for a major novel, Three Harbours, about the early phases of the American Revolution. By this time Mason was doing very well indeed as he was able to split his time between Nantucket, Bermuda, and Maryland. When delivering the manuscript from Nantucket, he was caught in the middle of the New England Hurricane of 1938 and had many close calls which may have ended his career right there. Fortunately the manuscript was a long one and he was able to use it as a defense against flying debris. He made it to New York and the book turned out to be very popular and changed his focus to historical fiction for the rest of his career, though he would continue to write Hugh North stories until 1968.
He wrote two more companion books to Three Harbours, Stars on the Sea and Rivers of Glory, as well as three more Hugh North mysteries in the years leading up to World War II. These books all did very well, especially Stars on the Sea which was a top 10 bestseller for 1940, and Mason was in his prime before the war interrupted his writing for a time. He reenlisted at the beginning of the war and suspended his writing career though he did manage to write some youth oriented war stories during the war under the name Frank W. Mason as well as publishing a couple of reworked pulp serials under the name Ward Weaver. During World War II he worked as Chief Historian serving on General Eisenhower's staff. His main responsibility was to document the war for future generations but he did lend a hand to write the famous communiqués which announced the activities of D-Day to the world. As part of his duties he followed behind or with advancing troops as they worked their way into enemy territory and was one of the first into some of the concentration camps including Buchenwald.
After the war he settled into a more leisurely pace of a little more than one book per year, which he was to maintain for the next quarter century. His style was well refined by this time and he was able to publish a string of fairly popular books. He finished his American Revolution series with Eagle in the Sky in 1948, wrote a popular novel about the famous buccaneer, Henry Morgan called Cutlass Empire in 1949, and started a trilogy on the Civil War in 1951.
He rewrote more of his pulps for the paperback market during the fifties and had a successful youth book called The Winter at Valley Forge in 1955. He would continue to write historical novels for the youth market after that as part of his mix. He also moved to Bermuda from the Baltimore area during the '50s. His wife was ill during this period and finally died in 1958.
He was soon remarried to Jean-Louise Hand, his long-time secretary. He spent the rest of his life in Bermuda, writing historical fiction for both the adult and youth market as well as several more Hugh North novels. He drowned off the coast of Bermuda in 1978 after having finished his final novel, Armored Giants, about the battle between the Monitor and Merrimack, which was published posthumously in 1980.