An ethics panel of eight House peers deliberated over two days before delivering a jarring blow to the 20-term New York Democrat's career. Rangel was charged with 13 counts of financial and fundraising misconduct.
The conviction also was another setback for Democrats who lost control of the House to the GOP in the midterm elections.
Rangel, a founding member of the Congressional Black Caucus, is not expected to resign. He is 80 years old and remains a dominant political figure in New York's famed Harlem neighborhood.
He was forced to step down last March as Ways and Means chairman when the House ethics committee, in a separate case, admonished him for taking two Caribbean trips paid for by corporations.
At his one-day trial on Monday, Rangel was reduced to pleading for a postponement - arguing that his lawyers abandoned him after he paid them some $2 million but could afford no more. The panel rejected his request, and Rangel walked out of the proceeding.
Only last spring, Rangel wielded significant power in the House from his position as the main writer of tax legislation. He was not present Tuesday when the verdict was announced.
The full ethics committee will now conduct a hearing on the appropriate punishment for Rangel, the silver-haired, gravelly-voiced and sartorially flashy veteran of 20 terms in the House.
Possible sanctions include a House vote deploring Rangel's conduct, a fine and denial of privileges.
The congressional panel, sitting as a jury, found that Rangel had used House stationery and staff to solicit money for a New York college center named after him. It also concluded he solicited donors for the center with interests before the Ways and Means Committee, leaving the impression the money could influence official actions.
He also was found guilty of failing to disclose at least $600,000 in assets and income in a series of inaccurate reports to Congress; using a rent-subsidized New York apartment for a campaign office, when it was designated for residential use; and failure to report to the IRS rental income from a housing unit in a Dominican Republic resort.
The ethics panel split 4-4 on a charge that Rangel violated a ban on gifts because he was to have an office - and storage of his papers - at the Charles B. Rangel Center for Public Service at City College of New York.
Two counts charging him with misuse of Congress' free mail privilege were merged into one.
The charges said the solicitation for the Rangel Center targeted foundations and businesses that were seeking official action from the House, or had interests that might be substantially affected by Rangel's congressional conduct.
However, Rangel was not accused of using his influence to pass or defeat legislation.
During Monday's trial proceeding, the chief counsel for the House ethics committee, Blake Chisam, told the jury that Rangel could have received permission to solicit nonprofit foundations. However, he could not have used congressional stationery and staff as he was found to have done.
Rangel had previously acknowledged some of the charges, including submission of 10 years' worth of incomplete and inaccurate annual statements disclosing his assets and income.
He also admitted he initially did not report his rental income from a unit he owned at the Punta Cana resort in the Dominican Republic.
An apartment in Harlem's Lennox Terrace complex housed the Rangel for Congress and National Leadership PAC political committees, when the lease terms said the unit was designated for living purposes only.
Chisam had told the jury that other tenants were evicted at an increasing rate for violating the same lease terms.