Australian-Indian engineer Naveen Rabelli, 35, had his passport and wallet stolen from his parked tuk tuk while he was in a toilet in Sarcelles, north of Paris.
This means he will have to wait for a new passport before crossing the English Channel and completing his journey, which began in India.
Rabelli set out on his epic 10,000 km road trip — from Kochi to London — across 10 countries on a zero-emission, hand-made, solar powered auto rickshaw in February.
He put his life savings into the project, which was designed to showcase a sustainable, low-cost alternative transport solution.
He connected with fellow environmentalists along the way and also recorded air-pollution levels in different countries.
The seven-month journey will end when he reaches Buckingham Palace, which he now hopes will happen on September 12.
"I have been on the road for seven months now, and have been dreaming to get to [the] UK. For four years I have been preparing for this," Rabelli told the BBC.
"It really sucks to have lost my passport and 1000 Euros."
So far Rabelli has travelled through Iran, Turkey, Greece, Bulgaria, Serbia, Austria, Germany and Switzerland, and has been helped by strangers along the way.
He purchased the tuk tuk for $1500 and spent $11,500 modifying it so that it is powered by electricity and solar power.
It also has a top speed of 60km/h.
"I named it Tejas because it means radiance," he told SBS.
"I want the world to know how this radiant idea was born."
When he has not been offered accommodation, he has slept in his tuk tuk, which also featured a bed and a solar cook top.
Born in India, Rabelli became an Australian citizen when he worked in Melbourne for three years as an automotive engineer.
He returned to India to pursue the project.