Families, students and campaigners descended on London for the march, which began in the heart of the financial district and snaked its way to parliament.
Brand and Church both received loud cheers as they spoke at a rally at the end of the protest — the biggest in Britain for several years.
The Welsh singer, 29, described the idea that Britain needs austerity as “the big lie” and said: “What this country needs is economic stimulation — most economists around the world would say the same. We need to get the blood pumping.” She called for the country to rally and “save ourselves from decades of yuppie rule”.
Brand was received with loud cheers as he took to the stage to speak after left-wing British Labour leadership hopeful Jeremy Corbyn.
The comedian spoke of his commitment to the anti-austerity movement and joked about his decision to back Labour days before the British general election.
The 40-year-old said: “Like most of you here I felt crushing disappointment on the morning after the election, unlike many of you I felt personally to blame for it.
“My personal feelings about this movement are very, very deep. Without a welfare state I wouldn’t have been educated, without a welfare state I wouldn’t have had anywhere to live, without a welfare state my mum would’ve died of cancer several times. I am personally a product of the welfare state — not least because I signed on for eight years while I learned to be a comedian, so somewhat grateful for it.”