Around 30 environmental activists clad in red and wearing climbing gear stood on ledges of the Europa building ahead of an EU summit on climate change on Thursday.
The group managed to climb the building by using the ladder of an old fire engine and have enough food to last for two days, according to Greenpeace spokesman Mark Breddy.
EU leaders are set to debate ways for the bloc to become carbon neutral by 2050. But poorer coal-dependent nations fear they could be hardest hit by the effort to transform their energy sources.
On Wednesday, European Commission President Ursula von der Leyen unveiled a new "European Green Deal" with an offer of some 100 billion euro (£84 billion) to help fossil-fuel reliant EU nations that make the transition to lower emissions.
The EU leaders will also discuss their long-term budget plans, the euro single currency and Brexit.