One in three children with a working single parent live in poverty, and the figure is set to increase in the coming years, according to a new report.
A study by the Gingerbread charity suggested that by 2021 almost two thirds of children in single parent families are likely to be living in poverty.
Jobs with decent pay and flexibility are "few and far between" for single parents who are the main earner and carer, said the report.
Single parents are more likely than the average worker to be "trapped" in low pay jobs and under pressure to take insecure employment, said Gingerbread.
Chief executive Rosie Ferguson said: "The findings of this report illustrate how single parents' aspirations can be thwarted by circumstances outside their control.
"The majority of single parents work but many are still locked out of the secure, flexible employment opportunities they need in order to provide for their children.
"Low-paid and insecure jobs, as well as the lack of affordable childcare, mean that some single parents struggle to put food on the table for their children.
"The government must work with job centres, employers and childcare providers to ensure that work genuinely provides a route out of poverty.
"We need to strengthen the system of support for single parents to provide a decent standard of living for them and their children."
Gingerbread urged the Government to expand childcare support to single parents in education or training and to offer help with upfront childcare costs.
Single parent employment rates are at a record high, but the numbers on zero hours contracts have increased tenfold in the past decade, the report added.
Debbie Abrahams, shadow work and pensions secretary, said: "It is utterly unacceptable that single parent families are paying the price for Conservative failure.
"The increase in child poverty is a direct result of this Government's cuts to social security, changes to universal credit and their complete failure to tackle the scourge of low-paid, insecure work."
A Government spokesman said: "We recognise how challenging it can be for lone parents to juggle work and family life. That's why we've taken steps to double free childcare, and for the most in need paying up to 85% of their childcare costs under Universal Credit, to support parents back into work.
"Children living in households where someone works are less likely to be in poverty and more likely to do well in school, compared to those growing up in workless households. Our support is all about ensuring every child and family has the best chances in life."