Deputy Assistant FBI Director Peter Strzok testifies on FBI and Department of Justice actions during the 2016 Presidential election during a House Joint committee hearing on Capitol Hill in Washington, DC, July 12, 2018.

FBI agent and former special counsel investigator Peter Strzok, whose anti-Trump texts have made him a pariah with the president and other critics of the Russia investigation, said Thursday that his actions at the agency were not motivated by his personal beliefs.

"Let me be clear, unequivocally and under oath: Not once in my 26 years of defending my nation did my personal opinions impact any official action I took," Strzok said in an opening statement at a public hearing in Congress before two House committees.

Strzok was aggressively criticized by Republicans on the House Judiciary and Oversight committees at the start of the hearing, which is expected to last all day and include questioning from dozens of lawmakers.

Strzok was called to testify about private text messages he sent as an FBI investigator, which were highlighted in a recent Inspector General report critical of the handling of a federal probe into Hillary Clinton's email server.

He worked on numerous high-profile and politically charged federal investigations, including the Clinton email probe — led by ex-FBI Director James Comey — and Russian involvement in the 2016 election. He also briefly worked on Robert Mueller's special counsel team as part of its investigation of potential coordination between the Trump campaign and Russia.

Strzok was removed from that investigation when Mueller found out about thousands of private text messages, some of which showed disdain for Donald Trump, sent to Lisa Page, a former FBI lawyer with whom he was having an affair.

Following opening statements from the committees' chairmen and ranking members, the hearing quickly devolved into a bout of bickering over parliamentary procedures in which both parties' lawmakers argued about whether certain questions were appropriate to ask Strzok.

After getting the green light, House Oversight Chairman Rep. Trey Gowdy, R-S.C., tore into Strzok over his texts about Trump.

"No wonder Bob Mueller kicked you off the investigation, Mr. Strzok," Gowdy said.

Strzok pushed back, saying he believed he was not removed from the probe because of his own bias, but rather "that it was done based on the appearance" of the texts. He accused Gowdy of misrepresenting that testimony. "I don't appreciate what was originally said being changed," Strzok said — to which Gowdy responded: "I don't give a damn what you appreciate."