Upon leaving school in 1967 Courtenay began a career with Charles Hill & Sons. He was then seconded to Bristol City Line in February of the same year, after which he worked under Dart Container line, Bibby, Furness Withy and finally for OOCL part of the Tung group, headed back then by C.H. Tung, formerly Chief Executive of the Hong Kong SAR. Courtenay also worked for an extended period in Hong Kong. Today Orient Overseas Container Line is headed by C.C. Tung.

Courtenay worked in various roles learning his trade from the bottom up in areas such as Documentation, Marketing and Sales before becoming a stalwart in the Trans-Atlantic Trade. He knew his trade inside out and was referred to by some as the ‘Oracle’ due to the depth of knowledge he possessed on the Atlantic trade. As Director of Transatlantic trade he was responsible for both US and Canadian services operating to and from Europe.

He had helped set up the Trans-Atlantic Agreement and its successor, the Trans-Atlantic Conference Agreement, and so was well-known member lines including Maersk, Sealand, P&O Nedlloyd, NYK Line, Hapag-Lloyd, Mediterranean Shipping Co and Atlantic Container Line. Courtenay had been closely involved with the long-running dispute between the European Commission and the Trans-Atlantic Conference Agreement that was finally settled shortly after his death.