Ammermüller was born in Germany and, like many drivers of his era, followed the standard ladder of domestic German junior series before entering international competition. His technical development within the Red Bull Junior Team framework gave him access to infrastructure and mentorship typically reserved for the most promising prospects in European junior motorsport.
In 2004, Ammermüller entered the German Formula Renault series, driving the number three car, and simultaneously competed in the Formula Renault 2000 Eurocup — a dual-series campaign typical of ambitious drivers seeking maximum track time in their formative years. The German Formula Renault series at that time was a proving ground for numerous future Formula One drivers, and Ammermüller's presence there placed him in direct competition with peers who would go on to Formula One careers.
He also competed in the Formula Renault 2.0 Italia series as part of his junior programme, building the mileage and racecraft that Red Bull's talent system required before elevating a driver into higher formulae.
By 2006, Ammermüller was racing in the GP2 Series for Arden International — the same team that had launched Vitantonio Liuzzi's F3000 title campaign two years earlier. His GP2 season was cut short when Christian Klien was dropped by Red Bull Racing for the final three Grands Prix of 2006 and the team's third driver, Robert Doornbos, was promoted to the second race seat. This created a vacancy: Ammermüller was elevated to third driver for the last three Grands Prix of the season, and he tested the Red Bull Formula One car for the first time on 14 September 2006, covering sufficient distance to meet the FIA Super Licence requirement.
For the 2007 season, Red Bull signed Ammermüller as a full-time test driver — a significant commitment that put him inside the Formula One paddock on a weekly basis. His 2007 GP2 campaign was disrupted by injury and he was replaced in certain rounds by Sébastien Buemi. When Sebastian Vettel's promotion to Scuderia Toro Rosso created a vacancy in the Formula Renault 3.5 Series, Ammermüller stepped into that seat, giving him high-level single-seater racing alongside his Formula One testing duties.
In 2008, he competed in the International Formula Master series.
Ammermüller represented Germany in the A1 Grand Prix series for the 2007–08 and 2008–09 seasons — a national-team format that gave drivers race opportunities outside the conventional European ladder. His 2007–08 season at Sepang was notable for a series of on-track incidents: he made contact with three different cars at turn two during the sprint race, resulting in disqualification from the feature race. The incidents earned him the wry nickname "Hammermüller" in paddock circles, though he recovered form to take his maiden A1 Grand Prix victory three weeks later at Zhuhai.
After his Red Bull chapter, Ammermüller transitioned to GT racing, competing in ADAC GT Masters for two seasons before joining the Porsche Supercup series in 2012 with Walter Lechner Racing. He found his competitive home in the Supercup, going on to win three consecutive titles in 2017, 2018, and 2019 — establishing himself as one of the defining champions of the one-make series in the late 2010s. His longevity in the Porsche programme demonstrated the racecraft developed during his junior single-seater years, even as Formula One ultimately remained beyond his reach.