The 56-year-old took an hour to clamber up the 230 meter (755 ft) Heron Tower in the city’s financial district.
Police kept crowds back as he worked his way up, using only chalk and muscle to get to the top.
A hobby that started when he was 11 has taken Robert to more than 150 skyscrapers around the world, including Dubai’s Burj Khalifa, the world’s tallest building, the Eiffel Tower, and the Sydney Opera House.
He often climbs without permission and has been arrested several times, sometimes for trespassing.
Police were waiting for Robert when he reached the top of Heron Tower. A spokeswoman for City of London police declined to comment on whether he had been charged with any offence.