Parliament passed legislation on Tuesday setting 2050 as the target but climate change campaigners want the deadline to be brought forward by at least five years.
The Bill amends the Climate Change Act of 2008, changing the emissions reduction target from 80% to 100%. It has now been passed to the House of Lords for final approval.
On Wednesday, up to 15,000 people were expected to turn out for the Time is Now mass lobby of Parliament calling for the target to be reached even earlier.
Dr Williams, who was there in his role as Christian Aid Chair, led people in a Walk of Witness from St Martin-in-the-Fields church in Trafalgar Square, past Downing Street to Parliament where they joined thousands of climate change campaigners.
He said: "Fewer and fewer people now doubt the urgency of our climate crisis, and a younger generation is showing us the way in resisting cynicism and passivity about this.
"It is imperative for people of faith to stand up and be counted – as witnesses to the sacredness of the world gifted to us by God, and as advocates in the cause of justice for all whose lives and livelihood will be most damaged by severe and unpredictable changes in climate."
The Walk of Witness was joined by the representatives of other faith groups.
The Roman Catholic Bishop of Salford, John Arnold, said MPs must reach the target on net zero carbon emissions "in the quickest and fairest way possible".
He also called on people of faith to keep those most affected by climate change "at the centre of our prayers".
Faith leaders took part in a Walk of Witness past Downing Street before joining thousands of climate change campaigners outside Parliament(Photo: Christian Aid)
"The Catholic community has been greatly moved by the injustice that communities overseas who have contributed least to greenhouse gas emissions now find themselves hardest hit by climate change," he said.
Imam Qari Asim MBE, Chair of the Mosques and Imams Advisory Board, said the time had come for the world's leaders to take "bold" action on climate change.
"The urgent threat to our earth, the water, the air and living things can no longer be ignored," he said.
"We can't continue to selfishly draw on exhaustible resources. The time is now to move beyond mere words and implement comprehensive set of climate solutions to reverse nature's decline.
"Political leadership across the world must take bold actions for the sake of future generations. The environment is God's gift to everyone.
"It is our individual and collective responsibility to take tangible and sustainable actions in our daily lives to protect our world and its inhabitants."
Rabbi Jonathan Wittenburg, leader of Masorti Judaism in the UK, delivered Radio 4's Prayer for the Day prior to taking part in the Walk of Witness.
He said that while mankind may not be harming the climate on purpose, it was nonetheless being "careless".
"Our habits of consumption and waste are killers, sometimes they cost human lives, they constantly cost the lives of animals, birds, insects, forests and rivers," he said.
"We can't escape our responsibility, we hold the light of creation in our hands."