After initially starting to train as an accountant, Donald moved to stockbroking in 1953.
In 1968 he became one of the 3,000 members of the London Stock Exchange, but was bought out when personal memberships ended and companies took over. He was a partner in several firms over the years, and became an expert in warrants, and later in traded options. In 1973, with the Ionian Bank, he floated an investment trust, Archimedes, which specialised in geared securities, and remained a director of the company for its life. During his career in the City he also became a Freeman of the City of London.
Donald was a founder committee member of ACTA (the precursor of the Society of Technical Analysts) and became its second chairman. He frequently lectured about charts and their uses in investment decision making. He retired in 1990 and died on 25 October 2014.