Diane Abbott told climate change activists in London that they had "done an amazing job".
Addressing a crowd of Extinction Rebellion protesters, the shadow home secretary praised their week-long protest, which including vandalising buildings and gluing themselves to DLR trains.
"I think you've done an amazing job drawing people's attention to the climate emergency," Ms Abbott said.
"In all the noise and kerfuffle of Brexit, the climate emergency is the most important issue facing us."
The Labour MP continued to praise the work of 16-year-old Swedish activist Greta Thunberg, who has become increasingly prominent in the discussion about climate change.
"I was very pleased to be in the room listening to our comrade Greta Thunberg. She was amazing, and I give her a lot of credit as a 16-year-old to go around the world and speak the truth to people twice and three times her age."