Koenig grew up in a tennis loving family and began at the age of five years with the tennis game. His uncle Gaetan Koenig in 1960 had played for the South African Davis Cup team in 1957 and moved into the second round of the French Open. From 1991, he first played on satellite tournaments and won his first match at the Challenger tournament in Johannesburg. The following year, he became a professional tennis player, reaching the third round of the ATP tournament in Washington. By this success he achieved with position 262 his highest individual listing in the tennis world rankings. In addition, he stood with the Swede Douglas Geiwald the doubles final of the Challenger tournament in Dublin. His first doubles title on the Challenger Tour he won in 1996 in Aachen. In 1999 he was in St. Pölten for the first time in the final of an ATP tournament in 2002 he celebrated his first title victory in Tashkent, followed by another tournament victory in Kitzbühel. Overall, he was able in the course of his career five ATP doubles title win six more times he stood in a final. Its highest listing on the double World Ranking position was 28 in 2003.
In individual he could qualify for a Grand Slam tournament, never, in the doubles competition was his best result of the semi-finals of the U.S. Open in 1998 at the site of John Laffnie de Jager. In mixed it reached in 2001 with Meghann Shaughnessy the semifinals of the Australian Open, in the following year he was with Els Callens in the semifinals of Wimbledon and the U.S. Open.
Koenig played between 2002 and 2003 three double matches for the South African Davis Cup team. All three games he could win each on the side of changing partners. For the 2004 Summer Olympic Games, the National Olympic Committee of South Africa decided to not report a double, although the common world ranking of Koenig and Chris Haggard participation could allow.