Hours before disgraced GOP Rep. Chris Collins was expected to plead guilty in Manhattan federal court to insider trading charges Tuesday, his resignation letter was read on the House floor.

Collins, who represents the Buffalo area, sent his resignation letter on Monday to House Speaker Nancy Pelosi and Gov. Andrew Cuomo.

“I hereby submit my resignation effective immediately, September 30, 2019, as United States Representative of the 27th District of New York,” ​Collins’ letter said.

​Collins is scheduled to appear at 3 p.m. ​to plead guilty, according to court filings and courthouse sources.

Collins was on the board of Australian biotech company Immunotherapeutics when he gave his son information in July 2017 about a failed trial of a drug developed by the company.

His son, Cameron Collins, and co-defendant Stephen Zarsky are expected to cop to unspecified charges on Thursday.

With additional reporting by Emily Saul, Carl Campanile and Bernadette Hogan