The first of two payments to help the poorest households with the cost of living will hit people's bank accounts from 14 July, the government says.
More than eight million UK homes on benefits will receive £326 by the end of July, with a second payment of £324 set to follow in the autumn.
It comes as part of a £37bn government package to help families as energy, food and fuel bills soar.
The consumer group Which? said the cash would "bring relief to many".
But policy director Rocio Concha added: "The success of these measures will ultimately be judged by whether financial help is getting to the most vulnerable in time to help them through this cost-of-living crisis."
