His father, Paul O'Neill, moved to London from New York in the 1960s to set up the European head office of Oppenheimer & Co, a New York-based investment bank. Paul O'Neill died in December 2004. His mother, Eva Maria O'Neill, is involved in a number of charities, with a particular focus on the cultural preservation of Salzburg, Austria.
Mr Christopher O'Neill and Princess Madeleine live in New York.
While growing up in London, Mr Christopher O'Neill attended Eaton House School and then Westminster Under School. In 1988 he began his studies at the Institut auf dem Rosenberg international high school in St. Gallen, Switzerland, graduating with a high school diploma in 1992.
Mr Christopher O'Neill began his undergraduate studies at Boston University that same year. Alongside his studies, he also worked for various financial firms on a part-time basis to develop work experience and to gain a practical understanding of the financial industry. In 1996, he obtained a Bachelor's Degree in International Relations and a Minor in Business Administration.
After his studies, Mr Christopher O'Neill returned to the UK. Here, he worked in the Mergers & Acquisitions department of NM Rothschild & Sons, before moving to an early stage venture capital firm, VennWorks LLP. At VennWorks, Mr O'Neill was responsible for the financial analysis of potential investments and for marketing the fund to institutional investors in Europe and the Middle East. As a result, he spent much of his time in Europe, the UAE and Kuwait.
After completing six years of post-graduate work experience, Mr Christopher O'Neill attended the two-year, full-time MBA programme at Columbia Business School in New York. Since graduating from Columbia in 2005 with an MBA degree, Mr O'Neill has worked as a securities analyst for both Steinberg Asset Management and Noster Capital. He has also invested in other entrepreneurial ventures.
Since his childhood, Mr Christopher O'Neill has had a strong interest in sports and outdoor activities, such as downhill skiing, tennis and golf. His other interests include music, literature, Chelsea Football Club and spending time with his family and close friends.
The engagement between Princess Madeleine and Mr Christopher O'Neill was announced on Thursday 25 October 2012.
The wedding took place on 8 June 2013 in the Royal Chapel at the Royal Palace of Stockholm.
On 20 February 2014 Princess Leonore was born.
On 15 June 2015 Prince Nicolas was born.
On 9 March 2018 Princess Adrienne was born.