Dr Barnes' principal achievements have been in the area of computer programming language design. He designed the language RTL/2 whilst with ICI. This was widely used in the 1970s and 80s for process control in the UK, the Netherlands and South Africa. The first ticket barrier system on the London Underground was an early example. He was a member of the Ada language design teams. Ada is widely used in safety critical applications such as those found in defence systems generally, avionics, air traffic control and railroad signalling. He has published twelve books: RTL/2 Design and Philosophy (1976); Programming in Ada (1982); Programming in Ada 95 (1996); High Integrity Ada (1997); Ada 95 Rationale (1997); High Integrity Software (2003); Programming in Ada 2005 (2006); Ada 2005 Rationale (2008); Gems of Geometry (2009); SPARK (2012); Ada 2012 Rationale (2013); Programming in Ada 2012 (2014). "Programming in Ada" went through four editions and was translated into six languages.

Dr Barnes has published many papers and given many lectures and tutorials on various aspects of programming. Although moving towards retirement he still gives occasional lectures including lectures for postgraduate courses. He has recently rediscovered an interest in mathematics and has given a number of popular courses at the Universities of Reading and Oxford as part of their Continuing Education programs; Gems of Geometry (now in a second edition) is based on one set of these courses.