Elijah Cummings was kept busy to the very end of his life leading an investigation into Donald Trump before passing away at the age of 68 on Wednesday, his aides have said.
The chairman of the House Oversight Committee was signing subpoenas from his hospital bed, one aide told the New York Times.
He also helped lead a Democratic caucus conference call.
House Speaker Nancy Pelosi described Mr Cummings as a “north star” who spoke with “unsurpassed clarity and moral integrity” on the House floor.
Ms Pelosi, who grew up in the city Mr Cummings represented, said he was her “brother in Baltimore” during a press conference on Thursday, adding: “We’ve all lost a friend … I’m devastated by the loss.”
Despite not having participated in a roll call vote since September, the late congressman was continuing to spearhead the oversight committee’s impeachment inquiry into Mr Trump along with two other House committees handling the investigation.
He has sparred with Mr Trump since the president took office, condemning the humanitarian crisis on the US-Mexico border during a fiery speech and decrying his attempts to ban residents of Muslim-majority nations from entering the country as “unconstitutional” and “un-American”.
Mr Trump consistently attacked Mr Cummings online, calling the congressman a “racist” then describing his majority-black district as a “disgusting, rat and rodent infested mess” in which “no human being” would wish to live.
Mr Cummings served 12-terms representing the 7th District of Maryland, which includes parts of Baltimore.
The president tweeted his “warmest condolences” to Mr Cummings’ family and friends, writing: “I got to see first hand the strength, passion and wisdom of this highly respected political leader.”
He added: “His work and voice on so many fronts will be very hard, if not impossible, to replace!”
The House announced its intentions to continue the impeachment inquiry against Mr Trump in the wake of Mr Cummings’ passing.
News of his death came as Gordon Sondland, the ambassador to the European Union, testified on Capitol Hill.
He turned on Mr Trump in a rare rebuke from a sitting ambassador and admitted he was “disappointed” by the president’s decision to have his Ukraine agenda go through his personal attorney, Rudy Giuliani.