Downing Street confirmed the Prime Minister backed French President Emmanuel Macron's push for the situation in the Amazon to be on the agenda when G7 leaders come together in Biarritz tomorrow.
Brazilian federal experts reported a record number of wildfires across the country this year - up 84% over the same period in 2018 - and environmental agencies have pointed the finger at the country's government for its relaxed policy towards deforestation.
Brazil contains about 60% of the Amazon rainforest and its degradation could have severe consequences for global climate and rainfall. The South American rainforest produces a fifth of the world's oxygen and fresh water.
A Number 10 spokeswoman said: "The Prime Minister is deeply concerned by the increase in fires in the Amazon rainforest and the impact of the tragic loss of these precious habitats.
"The effect of these fires will be felt around the world, which is why we need international action to protect the world's rainforests.
"The UK will continue to support projects in Brazil to do this and the Prime Minister will use the G7 to call for a renewed focus on protecting nature and tackling climate change together."
Mr Macron called the wildfires an international crisis and said the leaders of the G7 group of nations should hold urgent discussions about them during their summit on France's southwestern coast.
He tweeted: "Our house is burning. Literally. The Amazon rain forest - the lungs which produces 20% of our planet's oxygen - is on fire."
His comments were followed by an announcement from Berlin that German Chancellor Angela Merkel viewed the fires as "shocking and threatening".
But Brazilian President Jair Bolsonaro has hit back at his critics, accusing Mr Macron on Twitter of using a "sensationalist tone" that "does nothing to solve the problem".
In response to the fires, supporters of Extinction Rebellion UK, responsible for major climate change protests at Easter across British cities, have been gathering outside the Brazilian Embassy in London.
Amnesty International blamed the Brazilian government for the fires, which have escalated international concern over the vast rainforest that is a major absorber of carbon dioxide from the atmosphere.
Senior figures in the Labour Party have written to the PM to call on him to "immediately tell President Bolsonaro that his reckless destruction of the Amazon has to stop".
In a letter signed by the likes of shadow foreign secretary Emily Thornberry and shadow business secretary Rebecca Long-Bailey, the opposition ministers urged Mr Johnson to introduce "tough measures" to prevent UK companies from "aiding and abetting the destruction of the Amazon".
Labour leader Jeremy Corbyn told reporters: "Bolsanaro has allowed and indeed encouraged these fires to take place, to clear the forest in order that the land can then be used for actually very short term agriculture production and after that it becomes desert.
"That is what's happening to the rainforest. The rainforest is an international resource, it's a carbon sink that we all need and rely on."
Mr Johnson's show of support for discussions at the G7 follows criticism of one of his close allies for failing to publicly speak out during a trip to Brazil.
Labour's Barry Gardiner accused Trade Minister Conor Burns of "cosying up" to pro-deforestation ministers while on Government business and said he should instead have been calling on the country's right-wing leadership to do "everything they can to protect the rainforest".
Mr Burns posted on social media images of him drinking champagne with Brazilian minister Marcos Troyjo, who has backed President Bolsonaro's policy of deforestation of the Amazon.
The Conservative MP for Bournemouth West called Mr Troyjo "superb" after meeting him to discuss "increasing trade and prosperity" between Britain and Brazil.
A spokesman for the Department for International Trade said: "In meetings with the Brazilian government, Minister Conor Burns raised the UK's commitment to environmental protection and offered support to Brazil in the transition to renewable energy and a lower carbon economy."
Celebrities have joined the public outcry regarding the record number of forest fires in Brazil this summer.
The likes of singer Madonna, footballer Cristiano Ronaldo and Formula 1 champion Lewis Hamilton have spoken out about the fires raging in the rainforest.
The British racing car driver said: "More than a soccer field is being destroyed every minute everyday, the world needs to come together and help."