His apprenticeship supervisor was Polish advocate, Zdzisław Krzemiński, an expert in family and civil law and a supporter of Endecja.

Under Giertych's leadership, the LPR was successful in the European Parliament elections in June 2004, temporarily becoming the second-strongest Polish party with 14% of the votes.

In July 2004, Giertych was elected a member and vice-chairman of PKN Orlen investigation commission, which is credited, among other things, with destroying the presidential aspirations of Włodzimierz Cimoszewicz.

After losses in the elections of late 2007, Giertych stood down as leader of the LPR and left the party in 2009, which had already been deserted by most adherents such as Krzysztof Bosak and Robert Winnicki.

[12] He declared numerous times to vote for PO, co-founded several political initiatives and established himself as a busy investigator of embezzlement charges against PiS cadre,[13] while he is perceived critically in parts of the liberal public.

[23] He was the lawyer of the then head of the European Council, Donald Tusk, in an inquiry into the cooperation of Polish services with the Russian FSB.

The operation was represented to have benefited, among others, then-shareholder Ryszard Krauze, a fellow suspect and legal client of Giertych, who is a former billionaire struggling with bankruptcy since about 2010.

[33][34] On 20 July 2020, the European Commission mirrored a statement of the Polish National Bar Council indicating that defense lawyers acting in politically sensitive cases were intensively screened by the authorities.

[35] Giertych, together with fellow lawyers Jacek Dubois and Mikołaj Pietrzak, filed a complaint against Zbigniew Ziobro and his deputy to the International Criminal Court in The Hague.

[36][37] In late December 2021, Associated Press revealed that according to Canadian NGO Citizen Lab, the phone Giertych used in 2019 was infected by the Pegasus spy tool.

[42] In June 2022, the Parliamentary Assembly of the Council of Europe urged the European Commission to take a firm stance against the repression of political dissidents, as whom it identified Giertych.

[43] In July 2022, the European Commission published a report on the state of the rule of law in Poland that agreed with the aforementioned opinion.

[45][46][47] In January 2025 the Regional Prosecutor's Office in Lublin announced the discontinuation of the investigation concerning Giertych, while 8 out of 12 other suspects still await trial.