A prominent jurist and pro-democracy activist, Sólyom became the first president of the Constitutional Court at a time when the country was in the final years of its democratic transition after decades of communist rule.

During his mandate, the Court declared the death penalty unconstitutional, strengthened the protection of freedom of expression and conscience, and legitimated the domestic partnerships of homosexuals.

[3] In 1984, he completed another academic internship at the Max Planck Institute for Foreign and International Private Law and in 1988 he did research at the University of Frankfurt.

[3] He also participated in the meeting in Lakitelek [hu] on 27 September 1987 with other intellectuals opposed to the János Kádár regime and was one of the founding members of the then-illegal Hungarian Democratic Forum in 1989.

He was also a member of the Opposition Round Table Talks, which was a set of meetings to design the legal and political basis for post-communist Hungary.

[2][6] Throughout his legal career, Sólyom acquired a reputation for his academic accomplishments and for his doctrinal development of privacy rights.

[6][1] This led to his appointment as a judge of the newly established Constitutional Court of Hungary by the National Assembly on 24 November 1989, becoming its first president in 1990.

[5] In 2002, Prime Minister Péter Medgyessy appointed Sólyolm as head of the advisory committee of the bill to make public the collaboration of officials of the current government and administration with the secret police of the late communist regime.

[11] In March 2006 he refused to shake hands with János Fekete, former vice president of the Hungarian National Bank before the end of Communism in Hungary.

[14] On 26 June 2006, while the President of the United States George W. Bush was visiting Hungary to commemorate the fiftieth anniversary of the 1956 Hungarian uprising, Sólyom told him that "this fight against terrorism can be successful only if every step and measure taken are in line with international law", a comment that many media interpreted as a subtle criticism of the Iraq War.

He referred to the fact that Horn had not changed his views on the 1956 revolution in which he had taken part on the Soviet side, fighting against the Hungarian revolutionaries.

[17] In 2009, Sólyom was refused entry to Slovakia to attend the dedication of a statue of King Saint Stephen in the border town of Komárno on 21 August,[18] an incident reported in Hungary as tantamount to a declaration of persona non grata[19] which further worsened already tense Hungary–Slovakia relations.

"[20] Slovakia's government, containing the ultranationalist SNS party, claimed that the Hungarian President's presence is a "threat to national security".

[29] His funeral was attended by numerous politicians and public figures, including incumbent head of state Katalin Novák, former presidents Pál Schmitt and János Áder, house speaker László Kövér, cardinal Péter Erdő and apostolic nuncio Michael Banach, in addition to various members of the Hungarian government and opposition parties.