He was rushed to hospital, but died from his injuries.
Emergency services reported that the judge had started moving out to measure the javelin before it had landed, but that either a sudden gust of wind or a tragic misjudgement caused it to strike him.
"The official started walking towards the javelin before it had landed," said Michael Sandforth, Düsseldorf fire brigade spokesman.
"He was hit in the head, in the cheek and also sustained a wound to his carotid artery. He was bleeding very badly and lost a lot of blood."
The 15-year-old boy who threw the javelin was one of seven people at the event who was given counselling following the shocking events.
Strack was a highly experienced javelin judge, whose 18-year-old granddaughter Fiona is due to compete in the event at the German athletics championships in three weeks' time.
Some 300 athletes and 800 spectators were present at the meeting, which was immediately called off after the horrific accident.
A statement issued by the local athletics association paid tribute to Strack.
"He was a much-loved and experienced judge. All of us who were there are horrified and in shock," the statement said. "We will always remember Dieter Strack."
Accidents and fatalities are incredibly rare in athletics despite the apparent hazard caused by events such as the hammer and the javelin, with safety procedures always strictly adhered to. Early reports suggested that Strack had been going to measure a previous competitor's throw, but that was refuted by the fire brigade spokesman while police called Strack's death "the result of a tragic accident".
The last time a similar accident occurred was five years ago at a meeting in Rome, when French long jumper Salim Sdiri was speared through the upper body by a javelin.
The javelin narrowly missed one of his kidneys, but he recovered and returned to competition six months later. He went on to set the French record of 8.42m while winning gold at the 2009 Mediterranean Games.