The company was launched in February 2006 with a production called Home, staged on a bus in Aberdeen and was one of 10 site-specific theatre productions across the country.
Since then performances have taken place in various UK locations and around the world, including Los Angeles and Beijing.
The company, funded by the Scottish Government, has no permanent building and since 2006 has been involved in 200 productions at 174 locations, including airports, tower blocks, community halls and drill halls, ferries and forests.
Stephen Will, 17, became the millionth audience member by booking to see the National Theatre of Scotland and Royal Shakespeare Company's production of Dunsinane, which is touring the UK and opened at His Majesty's Theatre in Aberdeen last night.
The teenager, a pupil at Alford Academy in Aberdeenshire, is a member of Aberdeen Performing Arts (APA) Youth Theatre and is part of a group booking to see the performance.
He was presented with a special ticket to mark the milestone sale at the HMT box office in Aberdeen yesterday by actor Siobhan Redmond, who is playing Gruach in Dunsinane
Laurie Sansom, artistic director for the company, said: "We are delighted to celebrate our millionth member. Audiences are the life-blood of what we do as a company."
To mark the millionth ticket sale, one member of APA Youth Theatre will be selected at random to see the theatre's production of Let The Right One In at London's Royal Court Theatre.