There were tears from the 32-year-old, who missed the 2018 Games in February after failing to get fit in time following an illness, as he held a news conference in Trondheim on Wednesday to announce his retirement.
"It's been an adventure -- I had a little dream when I was a little boy that I would be a good skier and I'm proud to have achieved that. Cross-country skiing has been my life for so many years so it's tough to quit," he told reporters, his voice cracking with emotion.
"I have done my utmost to get back in shape and fight for a place at the World Cup in Seefeld but for the past two weeks I've felt that I'm too far behind, and then I chose not to spend more energy on it," Northug explained.
One of the most popular figures in Norwegian public life, Northug won two Olympic gold medals at the Vancouver Games in 2010 and a total of 13 world championship golds in a colourful and often controversial career.
His talent was recognised early, with sponsors queuing up to sign him as a teenager, and his brilliance on skis was matched by his sharp tongue, in particular when taunting rivals from Sweden to the delight of Norwegian fans.
In 2014 he was convicted of drunk driving, fined and sentenced to 50 days in prison after crashing his car near his home in Norway and fleeing the scene. The skier pleaded guilty and served his time by wearing an electronic tracking device.
Northug was given every chance to make the 2018 Olympic team but an illness derailed his plans and his efforts to regain fitness ahead of the current season were to no avail.
"I have lived in faith and hope that it could be turned around but the body can't take any more and the head is a little tired from what has happened before," he told reporters.
"This is the best solution for me and I believe I will be happy for that choice and look forward to new things."