Kaczyński was born in Warsaw, the son of Rajmund (an engineer who served as a soldier of the Armia Krajowa in World War II and a veteran of the Warsaw Uprising), and Jadwiga (a philologist at the Polish Academy of Sciences). As a child, he starred in a 1962 Polish film, The Two Who Stole the Moon (Polish title O dwóch takich, co ukradli księżyc), with his identical twin brother Jarosław.

Kaczyński married economist Maria Kaczyńska in 1978. They had one daughter, Marta Kaczyńska-Dubieniecka, and two granddaughters named Ewa and Martyna. His brother is Jarosław Kaczyński, the former Prime Minister of Poland.

Kaczyński was a graduate of law and administration of Warsaw University. In 1980 he was awarded his PhD by Gdańsk University. In 1990 he completed his habilitation in labour and employment law. He later assumed professorial positions at Gdańsk University and Cardinal Stefan Wyszyński University in Warsaw.

In the 1970s Kaczyński was an activist in the pro-democratic anti-communist movement in Poland, the Workers’ Defence Committee, as well as the Independent Trade Union movement. In August 1980, he became an adviser to the Inter-Enterprise Strike Committee in the Gdańsk Shipyard and the Solidarity movement. After the communists imposed martial law in December 1981, he was interned as an anti-socialist element. After his release, he returned to trade union activities, becoming a member of the underground Solidarity.

When Solidarity was legalized again in the late 1980s, Kaczyński was an active adviser to Lech Wałęsa and his Komitet Obywatelski Solidarność in 1988. From February to April 1989, he participated in the Round Table talks.

Kaczyński was elected senator in the elections of June 1989, and became the vice-chairman of the Solidarity trade union. In the 1991 parliamentary election, he was elected to the parliament as a non-party member. He was, however, supported by the electoral committee Center Civic Alliance, closely related but not identical to the political party Centre Agreement (Porozumienie Centrum) led by his brother. He was also the main adviser and supporter of Lech Wałęsa when the latter was elected President of Poland in December 1990. Wałęsa nominated Kaczyński to be the Security Minister in the Presidential Chancellery but fired him in 1992 due to a conflict concerning Jan Olszewski’s government.

Kaczyński was the President of the Supreme Chamber of Control (Najwyższa Izba Kontroli, NIK) from February 1992 to May 1995 and later Minister of Justice and Attorney General in Jerzy Buzek’s government from June 2000 until his dismissal in July 2001. During this time he was very popular because of his strong stance against corruption.

In 2001 he founded the political party Law and Justice (Prawo i Sprawiedliwość – PiS), usually labelled ‘conservative’ by media, with his brother Jarosław. Lech Kaczyński was the president of the party between 2001 and 2003. His brother Jaroslaw is its current chairman.

In 2002, Kaczyński was elected mayor of Warsaw in a landslide victory. He started his term in office by declaring a war on corruption. He strongly supported the construction of the Warsaw Uprising Museum and in 2004 appointed a historical panel to estimate material losses that were inflicted upon the city by the Germans in the Second World War (an estimated 85% of the city was destroyed in the Warsaw Uprising) as a direct response to heightened claims coming from German expellees from Poland. The panel estimated the losses to be at least 45.3 billion euros ($54 billion) in current value. He also supported the construction of the museum of Polish Jews in Warsaw by donating city land to the project.

Kaczyński banned the Warsaw gay pride parade twice in 2004 and again in 2005, locally known as the Parada Równości (the Equality Parade), stating that the application of the parade organizers had not been properly filed, and also that he did not respect homosexuals’ right to demonstrate, “I respect your right to demonstrate as citizens. But not as homosexuals.” Additionally, he feared the parade would promote a “homosexual lifestyle” and complained that police did not use enough force in breaking it up by stating “Why was force not used to break up an illegal demonstration?”. Kaczyński referred to the organizers of the gay pride parades as “perverts”. In 2004 his opponents called his actions unconstitutional and he was repeatedly criticized by the Mazowieckie Voivodeship administration, which officially supervises the Mayor of Warsaw.

In 2005, Kaczyński allowed a counter-demonstration, the “Parade of Normality”, organized by the All-Polish Youth, a Catholic nationalist organization opposed to “liberalism, tolerance, and relativism.”

On 19 March 2005, he formally declared his intention to run for president in the October 2005 election.

Elected President of the Republic of Poland (he defeated the runner-up Donald Tusk by polling 8,257,468 votes, constituting 54.04 percent of the vote), Kaczyński assumed office on 23 December 2005, taking an oath before the National Assembly.

From 2005 to 2007, in accordance article 133 of the Constitution of the Republic of Poland, Kaczyński pardoned 77 people and declined to pardon 550.

In November 2006 in Helsinki, at a European Union-Russia meeting, Poland vetoed the launch of EU-Russia partnership talks due to a Russian ban on Polish meat and plant products imports.

On 21 December 2008, Kaczyński became the first Polish head of state to visit a Polish synagogue and to attend religious services held there. His attendance coincided with the first night of Hanukkah.

Following the military conflict between Russia and Georgia in 2008, Kaczyński provided the website of the President of Poland for dissemination of information for blocked by the Russian Federation Georgian internet portals.

During a state visit to Serbia in 2009, Kaczyński said that the Polish government, on the basis of its constitutional competences, decided to recognize Kosovo and emphasized that he, as the President of the state, did not agree with that.

On 10 April 2010, a Tupolev Tu-154M plane was carrying Lech Kaczyński, his wife Maria Kaczyńska, and other members of a Polish delegation (top public and military figures) from Warsaw to commemorate the Katyn massacre. The plane crashed while approaching Smolensk Air Base in Russia. The governor of Smolensk Oblast confirmed to the Russia 24 news channel that there were no survivors. 96 people were killed in the crash, including many of Poland’s highest military and civilian leaders.

On 11 April 2010, President Kaczyński’s body was returned to Poland, where he and his wife lay in state at the Presidential Palace in Warsaw. The state funeral was held in Kraków on 18 April 2010. After a Roman Catholic mass at St. Mary’s Basilica, the presidential couple were laid to rest in a coffin, which was placed in the antechamber of the Crypt Under the Tower of Silver Bells beneath the Wawel Cathedral. A significant number of foreign dignitaries were unable to attend the funeral as a result of air travel disruption in Europe following the eruption of the volcano Eyjafjallajökull in Iceland.

In June 2016, the Polish government announced it would re-open the investigation into the Smolensk jet crash with plans to exhume and autopsy all 96 of the victims. On 14 November 2016, the first of ten bodies, including Kaczyński’s, were exhumed. Kaczyński and his wife were reburied on 18 November 2016 after autopsies.