Simpson was born in Christchurch, New Zealand, and raised in the Waikato. He attended high school in Christchurch and in 1967 began his career as a computer programmer, at age 18.
In 1969 he wrote the initial direct debit and direct credit applications which are in common use throughout the New Zealand banking industry today. By age 22 he was Head of Computer Programming at the Comalco aluminium smelter in Bluff, which at that time was the largest industrial project ever undertaken in New Zealand.
He returned to Christchurch around 1972, making it his home permanently. He lived in Jeddah, Saudi Arabia, working as a programmer for Caterpillar Inc. between 1976 and 1978, after which he returned to New Zealand to develop a new concept in computer programming through his creation of the fourth generation language known as LINC. LINC remains New Zealand's most successful software export to date. He has resided in Christchurch ever since, where there is now a street named after him Sir Gil Simpson Drive.
Simpson is the founder of the Aoraki Corporation (later known as Jade Software Corporation), developers of the LINC 4GL and Jade programming language , who are also well known for their past sponsorship of Christchurch's Jade Stadium. More recently he founded Jolly Good Software Pty Ltd in 2006 .
Honours and awards
In the New Year Honours 2000 Simpson was appointed a Knight Companion of The New Zealand Order of Merit for services to information technology, commerce and the community'. Later in 2000 Simpson was chosen to receive The New Zealand Computer Society's Supreme Award for the most outstanding contribution to computing in New Zealand in the 20th century.  In 2005 he was inaugurated into the New Zealand Business Hall of Fame, an honour reserved for business leaders responsible for outstanding contributions to the nation. In 2008 Simpson received an NZX Flying Kiwi Award and joined the PricewaterhouseCoopers NZ Hi-Tech Hall of Fame. Simpson has also been a director on the board of the Reserve Bank of New Zealand, as well as that of numerous other companies, both public and private.
With many outstanding achievements his profile in information technology has accorded him:
- An honorary doctorate from the University of Canterbury, D.Sc (h.c.)
- Past presidency of the Royal Society of New Zealand, of which he is now an honorary member
- Chairman of the New Zealand government's E-Commerce Action Team
- Chair of the New Zealand E-Commerce Summit, 2000
- Chairman of the Christchurch City Mission
- Associate membership of the New Zealand Business Roundtable 
- Fellow of the New Zealand Institute of Management, and past membership on the NZIM advisory board
- Fellow of the New Zealand Institute of Directors
- Honorary Fellow of the Institute of IT Professionals
- Founding patron of the Royal District Nursing Service, Australia 
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