He joined worshippers at One Church in Brighton before a climate change prayer vigil on Brighton beach.
The church service is a traditional Labour Party event at the beginning of the annual conference, organised by Christians on the Left.
Mr Corbyn heard how Church groups are campaigning for more action on climate change, with representatives from Tearfund, CAFOD and Christian Aid all there.
Songs of Praise was exactly right to go to Calais. @jeremycorbyn #Lab15 pic.twitter.com/BruZ2cCqWv
— krish kandiah (@krishk) September 27, 2015
Andy Flannagan, director of Christians on the Left, said: "Christians are at the forefront campaigning on poverty and climate change issues. The climate change talks taking place in Paris soon will be crucial for the future of the world. That's why we chose this theme for the service. We are delighted that Jeremy will be joining us."
The main speaker was Krish Kandiah, from the London School of Theology. who said there had been a "really encouraging turnout".
Jeremy Corbyn also told the crowd he thought BBC show Songs of Praise was right to go to Calais.
Seaside vigil for those effected directly by climate change #ForTheLoveof pic.twitter.com/HCpIUaIv5Y
— krish kandiah (@krishk) September 27, 2015
The TV programme faced criticism for the decision to film an episode at a makeshift church in a refugee camp in the French town.
Elsewhere Jeremy Corbyn has called for the end to the UK's "weapons of mass destruction" as the Labour Party conference prepared to vote on the future of the nuclear deterrent.
The Labour leader acknowledged that he may be unable to persuade members of his shadow cabinet to oppose the renewal of the Trident weapons system and there may be a "difference of opinion" when the parliamentary vote takes place.