The 57-year-old scaled the Cheung Kong Centre, owned by billionaire Li Ka-Shing, before hanging the banner with the Hong Kong and China flags above a handshake.
Prior to the stunt, Robert issued a statement saying his climb was "an urgent appeal for peace and consultation between Hong Kong people and their government".
"Perhaps what I do can lower the temperature and maybe raise a smile. That's my hope anyway," the 57-year-old said. He was arrested by the police after the climb, according to Efe news.
Also, Li who owns the Cheung Kong Centre put out a number of ads in Hong Kong newspapers, urging an end to the past weeks' violence. He called on people to "love China, love Hong Kong and love yourself" and to "cease the anger with love" and "stop the violence".
Hong Kong has seen months of anti-government protests that sometimes led to violent clashes with the police. The protests were sparked in June in opposition to the government's contentious extradition bill that was later shelved by Hong Kong Chief Executive Carrie Lam after intense pressure.
The controversy surrounding the now-defunct extradition bill, which would have enabled fugitives to be transferred from Hong Kong to mainland China to stand trial under the latter's opaque legal system, has morphed into a set of wider demands for democracy in the ex-British colony.
The Frenchman has made a name for illegally climbing skyscrapers across the world, often without safety equipment.
Almost exactly a year ago, Robert was banned by a Hong Kong court from making any more climbs after he was charged over a 2011 illegal ascent of the 27-floor Hang Seng Bank building to raise awareness about global warming.
At the time, he joked he would be back on day 366, the South China Morning Post reported.
His Friday stunt met mixed reaction online.
Australia-based Chinese dissident artist Badiucao asked on Twitter: "Do you really want (to) shake hands with butchers and dictators?"
"This shows many foreigners don't understand the underlying issue between Hong Kong and China," said another user.
Earlier this year, Robert was arrested in the Philippines after climbing a 47-storey tower in the capital, Manila.
His past feats include climbing the Burj Khalifa tower in Dubai, the Petronas Towers in Kuala Lumpur, the Taipei 101 building in Taiwan and the Heron building in London.
( With inputs from IANS )