Plan International UK generated £4.6m from a new partnership with the People's Postcode Lottery, which helped to end two years of declining income, according to its latest accounts.
The accounts, which were filed with Companies House this week, showed the global children's charity had an income of £66.7m in the financial year ending 30 June 2018.
This was £2.4m up on the previous year's £64.3m income but still down on £70.2m in 2016 and £80.4m in 2015.
Plan International UK became one of 30 direct beneficiary charities of the People's Postcode Lottery, which runs society lotteries on its behalf, in December 2017.
"These results represent a significant success in a year in which securing income continued to be challenging," the accounts say.
"Our new relationship with the People's Postcode Lottery is in line with our strategic goal to develop diverse and effective partnerships."
The accounts also reveal that Plan International UK received 147 fundraising complaints in the 2017 calendar year, down by 46 per cent on the 272 complaints received in 2016. Sixty-five per cent of complaints related to direct mail.
Alan Gosschalk, director of fundraising at Plan International UK, said: "We have recently implemented a number of new processes to improve our supporter relations, including enhanced staff training, mystery shopping of our door-to-door fundraisers and a renewed commitment to responding rapidly to phone calls and emails.
"We believe these improvements, combined with more positive public attitudes towards fundraising, have helped us to significantly reduce the number of complaints we receive."
The accounts show that 11 per cent of income was spent on fundraising activities and 8 per cent on support costs.
Tanya Barron, the chief executive, was the highest-paid employee. She received £116,500, made up of a gross salary of £101,156 and a salary sacrifice of £15,344.
She announced in January that she would retire in June after six years in the role.