After apprenticeships in British shipyards and aircraft manufacturers, Kennedy set up a boat design and manufacturing business in England. He worked on naval craft during the Second World War, after which he became a successful yacht and dinghy designer in Britain. His next career was in Bombay where he was involved with the design of tugs, harbour launches and fire fighting vessels. Kennedy then returned to Ireland and the River Shannon in 1960. He was the first to see the potential of the Shannon for hire cruising and he 'invented' the river as a popular tourist destination. He designed and built his own fleet of hire cruisers, and also found time to design the Kerry class of yacht, and compete in the Round Britain and Ireland race.
Kennedy published an autobiography "Not all at Sea!" in 1997.