Warnecke was a specialist in the breaststroke short routes. On the short course in 1995 he became world champion for the first time over 100 m breaststroke. At the 1996 Summer Olympics in Atlanta, he won the 100m breast the bronze medal, this was by 2005 his greatest success on the long course. Warnecke launched for SG Essen.
The long-time active speaker of the German Swimming Federation had announced in spring 2005 that he as fit as long no longer felt that he had been spared a prolonged time from injury problems. He attributed this to the fact that he had placed in abandoning the classical training plans more emphasis on competition endurance and short-term endurance. In the swimming world championships in 2005 in Montreal, he won the gold medal in the 50m breaststroke and is at the age of 35 years, the oldest world champion in the history of swimming sport since 1971. At 36, he won for the tenth time the German championships over 50 m breaststroke.
According to him, he owes his success to a proprietary amino acid preparation.
On April 14, 2007, during the 119th German Swimming Championships he finished his swimming career.
In order to reduce his body weight for the competition, he developed his own diet, which he now sells commercially.