Focus Ireland says it supported a record number of more than 15,500 people last year who were homeless or at risk of homelessness, including 1,600 families.
The figure represents a 7% increase on the 14,500 people the charity helped in 2017 and a 14% rise on the number in 2016, when over 13,500 people were supported.
The charity's annual report for 2018 also says it helped over 500 families to leave homelessness, in conjunction with the State, and it says it prevented almost 600 households from losing their home.
Focus Ireland says it provided 176 homes last year and served more than 44,000 hot meals to homeless people.
The latest homeless figures from the Department of Housing, published earlier this week, show there were 10,275 people in emergency accommodation in July.
While the number of adults remained static at 6,497, the number of children rose to 3,778, an increase of 103 on the previous month.
Focus Ireland says the figures show the homelessness crisis is continuing to deepen.
The charity has launched a new campaign to highlight a 356% increase in the number of homeless children across the country over the last five years.
The figure increased from 828 in September 2014 to 3,778 in July of this year.
Life-size images of children are being projected onto buildings in Dublin as part of the campaign.
Rachel Murphy, Co-Director of Fundraising at Focus Ireland says: "we want to make sure that people realise just because they don't see children on the street, it does not mean there aren't thousands homeless."
The charity says more than one in three people in emergency accommodation is a child.
Pat Dennigan, the Chief Executive of Focus Ireland, says "a lot of those children are back to school this month and are going to school from hotels and B&Bs, and I find that unacceptable."
Despite a fall in the homeless numbers in May and June, he says the homeless figures for July show "the trend is going in the wrong direction and the trend is something that we are concerned about."