More than 6,500 people will be in homeless accommodation by the end of the year, almost double the number from the start of 2015, said Fr Peter McVerry.
The campaigning priest said homelessness would continue to get worse in the months ahead.
Fr McVerry said the Coalition needed to acknowledge the scale of the problem and declare a national emergency.
Fr McVerry said at the current rates of increase there would be 6,519 in homeless accommodation across Ireland by the end of the year, an increase of almost 50 per cent since January this year.
“It is escalating out of control. Another 400 families will be homeless before the next election, if its in spring,” he said.
He added that the 150 modular housing units scheduled for delivery before Christmas were not enough to cover the number of additional homeless families for August and September.
“With this type of inadequate response we have no option but to question whether this Government are committed to helping people in homelessness,” Fr McVerry said.
He said an average of 70 families a month became homeless in Ireland.
“They’re not coping. An entire family living in one room with no access to cooking facilities or laundry. It puts a huge strain on relationships,” he said.
“The private rental sector is no longer the solution, it is the cause behind homlessness.”
The charity launched its pre-budget submission in Dublin on Wednesday.
Fr McVerry said the Taoiseach or the Tánaiste should take responsibility for co-ordinating the multidepartmental effort required to tackle the problem.
He has also called on the Government to hold a referendum on the right to housing.
Pat Doyle, chief executive of the Peter McVerry Trust, said "we need urgent action to tackle this emergency.
“We are worried about the months coming up to Christmas.
“ Peter McVerry Trust believes that rapid investment in housing must be prioritised to get people out of homeless accommodation. Housing, not shelter, is the answer to this emergency.”
The submission also called for rent certainty, reintroduction of higher quality bedsits and an increase in funds to bring derelict buildings back to use.
