"Despite so many false statements and lies, total and complete vindication...and WOW, Comey is a leaker!" he tweeted early on Friday.
Mr Comey told Congress under oath he believed he was fired to influence his investigation into the Trump campaign.
The ex-FBI boss led one of several Russia inquiries before he was sacked.
It is not clear what falsehoods Mr Trump is referring to but his lawyer has rejected as untrue several key parts of Mr Comey's testimony.
Mr Comey, who testified before the Senate Intelligence Committee on Thursday, said the president pressured him to drop an investigation into former national security adviser Michael Flynn.
Mr Flynn was himself forced out after misleading the vice-president about conversations with Russia's ambassador before Mr Trump took office.
Mr Comey also said the president defamed him and the FBI by claiming the agency was "poorly led", which Mr Comey called "lies, plain and simple".
He said he began writing memos after his meetings with Mr Trump because he was "honestly worried he might lie".
He leaked details of his memos after an account of it had already been published in the press.
As a result of that episode, a special counsel was appointed to lead an independent investigation into the Trump campaign's potential ties to the Kremlin.
But there is no known evidence of collusion between Russia and the US, and President Donald Trump has dismissed the story as "fake news".
After the hearing, the president's personal lawyer issued a statement rejecting many of Mr Comey's allegations.
Marc Kasowitz said on Thursday that the president never sought to impede the investigation into possible Russian interference in the US election and that Mr Comey's leaks should be investigated.
He also said the testimony confirmed that Mr Trump was not under investigation as part of any probe into Russian political meddling.
Hours later, Mr Trump ignored reporters when asked about whether Mr Comey was telling the truth.
US President Donald Trump has broken his Twitter silence after James Comey's explosive testimony to appear to accuse the former FBI chief of perjury.