Michlmayr joined the Debian project in 2000.[1] In 2003, Michlmayr was elected as Debian Project Leader;[2][3] he was re-elected to that position one year later, in 2004.[4][5]
Michlmayr contributed to Debian's New Member process, participating in the recruitment of over 120 new members.[6] Additionally, Michlmayr made various contributions to Debian's quality assurance effort. He identified the problem of packages with inactive maintainers and implemented processes to address this problem systematically.[7] He also became involved in identifying inactive maintainers whose packages should be reassigned; created overviews of bugs in Debian; and coordinated keysigning to improve Debian's web of trust.[8] He also contributed to Debian's ports to the ARM and MIPS platforms, by porting Debian to several embedded devices and Network Attached Storage (NAS) devices. He used snapshots of the GCC compiler to build the entire Debian archive. This work resulted in the identification of compiler bugs as well as build errors in many open source packages.[9]
In 2013, O'Reilly awarded an open source award to Michlmayr, putting him in "the 'unsung heroes' category—the people who devote themselves to the important but not always glorious jobs that keep open source healthy".[11]