The company Praxis Systems Limited was founded by Martyn Thomas and David Bean in 1983. It was incorporated on June 1, 1983 and commenced business on July 1, 1983. On June 28, 1985 it became a Public limited company Praxis Systems plc. Until 1988 Praxis was owned almost entirely by its staff. In 1988 Praxis obtained venture capital finance in order to provide funds for future acquisitions and working capital for continued growth. On November 27, 1992 Praxis was acquired by Deloitte Consulting (then known as Touche Ross), an international firm of accountants and management consultants. The critical systems part of the company was acquired by the Altran Group in 1997. In 2004, Praxis Critical Systems and HIS Consulting merged to form Praxis High Integrity Systems, a leading specialist in critical systems engineering.
A distinguishing feature of the company is its extensive use of formal methods such as the Z notation and the SPARK toolset (acquired through the takeover of the developers Program Validation Limited in 1993) in its approach to improving the reliability of software engineering. A major project using Z has been a small piece of the United Kingdom's National Air Traffic Services (NATS).