Werner Müllner began studying Journalism & Communications Science at University of Vienna in 1978. He had his first taste of working at APA in 1979 during a holiday work placement, after which he spent several years freelancing for the arts & culture department and later on the current affairs desk. After taking a role as Press Spokesman for the Traffic Safety Agency, he returned to APA at the end of the 80s. In 1998 he was given the role of Manager Current Affairs. He held this position until 2005 when he became News Manager and since 2008, Deputy Editor-in-Chief. 

In addition to his position as Deputy Editor-in-Chief, Müllner is Director of the APAcademy Newsroom and Coordinator for internal APA Quality Projects. 

He also acts as the interface between the newsroom and IT at APA. For some time he has been a trainer for the APA-Campus (Writing Workshop), as well as for the KfJ College Salzburg und the Tyrolean Journalism Academy, among others. As project manager for the Austrian Video Platform (AVP), he leads its development as an independent platform for sharing video content between media companies in Austria.