The Taoiseach is living in denial on the homelessness crisis, Mary Lou McDonald said.
Tens of thousands of people are living in misery as a consequence, the Sinn Féin leader said, ahead of a major protest in Dublin on Saturday.
More than 6,000 adults were affected in February, mostly in Dublin, Department of Housing statistics showed.
Ms McDonald said: "The fact is that we have a Government in denial, the fact is that we have a Taoiseach and a minister for housing living in denial, the fact is that countless tens of thousands of people as a consequence are living in misery and I think the numbers of the streets today will tell you that the Government is out of time on this issue."
Leo Varadkar has previously said he is frustrated by rising homelessness, but is working to address the problem.
The Government has previously accused Sinn Fein of turning a significant issue into a party political one.
In February, the number of homeless adults was 6,052, up 24% on the same month last year, and up 4% on January 2018, a monthly increase of 215.
Ms McDonald said child homelessness was up 50% over the past 12 months.
She added: "A shocking 488 children became homeless just last February. That is the single biggest increase in child homelessness on record."
She said the Taoiseach and the Minister for Housing Eoghan Murphy must work to tackle rising rents and stop evictions.
"This is what a Sinn Féin minister for housing would do. A Sinn Féin minister for housing would also declare a national housing emergency, legislate for real rent certainty and invest more in social and affordable housing."
Hundreds if not thousands of people attended the Dublin anti-homelessness demonstration.
The march - organised by the National Homeless and Housing Coalition - began at the Garden of Remembrance and ended at the Customs House.
— Andrew Lowth (@AndrewLowth1) April 7, 2018
Demonstrators carried placards criticising vulture funds and messages highlighting child homelessness.