The funding is part of a £225m national emergency active travel fund intended to help towns and cities provide clean alternatives to public transport during the Covid-19 crisis.
Guidance issued by the government made it clear that only "meaningful" plans which changed the "status quo on the road" would receive money from the fund.
Extinction Rebellion Brighton, along with other groups, has campaigned for better, 'game-changing' facilities for cycling and walking in the city, including segregated cycling infrastructure.
Paul Taylor a spokesperson for Extinction Rebellion Brighton, said:
"Extinction Rebellion Brighton are delighted the council's funding bid has been successful.
"The government made it clear that it would only fund schemes that made big, meaningful changes to the current use of road space.
"So, winning this money is testament to the boldness of the council and to the campaigning efforts of a diverse range of groups.
"The efforts of Extinction Rebellion were among several initiatives highlighting the benefits of active travel.
"These included celebratory cycle rides, petitions and emails to councillors.
"There is a clear desire across Brighton for the future of the city post-lockdown to be markedly different.
"People are no longer prepared to put up with streets choked with cars that emit toxic pollution and fuel the climate crisis.
"They want a cleaner, healthier, safer space in which to live, travel and work.
"We are pleased that the council has recognised that and acted on it by coming up with some exciting plans.
"We look forward to them coming to fruition and hope they are the start of a transformation of the way people get about in our city – something that is needed if we are to tackle pollution, climate change and meet the target of net zero emissions by 2030."
The money is intended to boost cycling and walking levels immediately as lockdown is eased.
The council has also been earmarked a further £2.4million from the fund for more permanent measures which would help "embed walking and cycling as part of new long-term commuting habits and reap the associated health air quality and congestion benefits".