Daniel Koellerer was born August 17th, 1983 in Wels Austria, and turned professional in 2002. He achieved his career-high ranking of number 61 on August 24th, 2009.
Kollerer reached a Juniors career high of number 23 in singles and number 24 in doubles in January, 2001, also in 2001, he beat future pros John Isner and Jo-Wilfried Tsonga. He earned his first ranking points as a 16-year-old wild card entry in his first pro tournament, a Futures tournament in Austria in May, 2000, losing to #520 Kristian Pless in the quarterfinals. He slipped from the rankings a year later, but began to rise slowly after turning pro in 2002. A Futures championship in Jamaica in November, 2002 helped him end 2002 ranked #640 as a 19-year-old.