Rep. Charles Rangel was convicted on 11 counts of ethics violations by a panel of his peers, Tuesday, and will now face penalties.
The eight-member House ethics panel deliberated for two days before finding the 20-term New York Democrat guilty.
Rangel, 80, was originally charged with 13 counts of financial and fundraising misconduct. He called Tuesday's decision "unprecedented."
"How can anyone have confidence in the decision of the ethics subcommittee when I was deprived of due process rights, right to counsel and was not even in the room?" Rangel said in a written statement.
"I can only hope that the full committee will treat me more fairly, and take into account my entire 40 years of service to the Congress before making any decisions on sanctions," he said.
Rangel walked out of the hearing Monday, claiming he was not given enough time to secure legal council. The hearings continued without him.
Rangel is former chairman of the Ways and Means Committee, but was forced to step down last March when, in a separate case, a House ethics committee admonished him for taking two Caribbean trips paid for by corporations.
Among other things, the ethics panel found that Rangel had used House stationery and staff to solicit money for a New York college center named after him. He also failed to disclose at least $600,000 in assets and income in a series of inaccurate reports to Congress.