Van Veldhoven started his career with local youth team De Raven. He was picked up by SK Lommel at the age of 17. He made his way up to the highest level of Belgian football with Germinal Ekeren. He then went to RWDM and eventually returned to SK Lommel when they had also arrived in First Division. The 3 teams for which van Veldhoven was active as footballer at senior level, are already all defunct.
When Harm van Veldhoven finished his playing career with Lommel, he became assistant coach. It only took him one season to become head manager of the team. Afterwards, he was manager for FC Brussels with which he became champions. This success woke the interest of Cercle Brugge, where he stayed 3 years. When his contract ended, van Veldhoven went to Germinal Beerschot, of which his former team Germinal Ekeren was a predecessor. After a very successful season, he could not repeat his achievement and was sacked as a consequence. He went back to his country of birth and signed for Roda JC in November 2008. He avoided relegation after play offs. His contract ended in 2012, which allowed him to sign with KV Mechelen, where he was sacked on 30 December 2013.