Smith testified behind closed doors last month but returned to the House Judiciary Committee for a public hearing, his first since leaving the job last year.
The hearing split along partisan lines as Republican lawmakers sought to undermine the former Justice Department official as Democrats hoped to elicit new and damaging testimony about Trump's conduct.
"It was always about politics," said Representative Jim Jordan of Ohio, the Republican chairman of the House Judiciary Committee.
"Maybe for them," retorted Representative Jamie Raskin, the panel's top Democrat, during his opening statement.
"But for us, it's all about the rule of law."
Smith told lawmakers that he stood behind his decision as special counsel to bring charges against Trump in separate cases that accused the Republican of conspiring to overturn the 2020 presidential election after he lost to Democrat Joe Biden and hoarding classified documents at his Mar-a-Lago estate in Palm Beach, Florida after he left the White House.
He said that, as special counsel, he had "followed Justice Department policies, observed legal requirements and took actions based on the fact and the law".
"Our investigation developed proof beyond a reasonable doubt that President Trump engaged in criminal activity," Smith said.
"If asked whether to prosecute a former president based on the same facts today, I would do so regardless of whether that president was a Republican or a Democrat."
"No one should be above the law in our country, and the law required that he be held to account. So that is what I did," he said.
Republicans sought to portray Smith as an overly aggressive hard-charging prosecutor who had to be "reined in" by higher-ups and the courts as he pursued Trump during his campaign.
They pressed Smith on the decision to seek and review phone records of more than a half-dozen Republican lawmakers who were in contact with Trump on the afternoon of January 6, 2021 as his supporters stormed the Capitol in a bid to halt the certification of his 2020 election loss.
The records revealed the length and time of the calls but not the content of the communications.
Smith said collecting phone records was a "common practice" and said he sought the data because he wanted to understand the "scope of the conspiracy" to overturn the election.
Smith was summoned to the hearing by Jordan, who suggested the investigation was driven by a desire to derail Trump's candidacy.
"We should never forget what took place, what they did to the guy we the people elected twice," Jordan said.
Smith vigorously rejected that and said the evidence placed Trump's actions squarely at the heart of a criminal conspiracy to undo the 2020 election.
"The evidence here made clear that President Trump was by a large measure the most culpable and most responsible person in this conspiracy," Smith said.
"These crimes were committed for his benefit. The attack that happened at the Capitol, part of this case, does not happen without him. The other co-conspirators were doing this for his benefit."
Trump pleaded not guilty to all charges and has repeatedly argued the charges were improperly aimed at damaging his 2024 campaign.
Neither case reached trial and Smith dropped them after Trump won re-election, citing a Justice Department policy against prosecuting a sitting president.
Trump's administration has fired dozens of Justice Department lawyers, FBI agents and staffers who worked on the investigations.
It was unlikely that Smith would share new information on Thursday about his classified documents investigation.
with Reuters
