The actor – believed to be worth about £7m – joins a list of wealthy people calling for governments to tax the rich more heavily.
Other signatories include the Notting Hill and Love Actually screenwriter Richard Curtis, Richard Reed, co-founder of Innocent Drinks, and the former chief executive of Unilever, Paul Polman.
Pegg, 49, whose films include Hot Fuzz and Run Fatboy Run, describes inequality as a “policy choice” and “not inevitable”.
He says half the world’s population is trying to survive on £4.20 a day or less, according to estimates, and that the “rate of poverty reduction has halved since 2013”.
Meanwhile, the number of billionaires has doubled in the last decade, he writes in The Times.
Taking a dig at world leaders, he says that fixing the “broken economy” might “feel too complex” for them.
He adds: “So let the millionaires help get you started. Tax them. Tax them more and do it now.”
Pegg describes inequality as the “driving force behind both societal breakdown and the very real climate crisis we face”.
The law in many countries is “so full of loopholes”, Pegg says, that a “billionaire can legally pay a lower rate of tax than his assistant, and a multinational company can pay less tax than a corner shop”.
The letter he has added his name to has attracted more than 120 signatures.
It claims that in “many nations, tensions caused by inequality have reached crisis levels”.
It adds that “most reasonable people understand that philanthropy has always been, and always will be, an inadequate substitute for government investment”.
In continues: “Taxes are the best and only appropriate way to ensure adequate investment in the things our societies need.”
People who “refuse to be part of the solution” will “be to blame”, it concludes.