With the CHP shut down during the 1980 Turkish coup d'état, Baykal was briefly imprisoned before being elected to Parliament once again in 1987 from the new Social Democratic People's Party (SHP).

He was re-elected leader in September 1995, after which Baykal contested the 1995 general election and formed a coalition government with Tansu Çiller's True Path Party.

As the oldest MP in Parliament following the June 2015 general election, Baykal briefly served as the interim Speaker of the Grand National Assembly.

He was noticed by senior officials of the CHP after writing a detailed analysis of the party's defeat in the 1965 general election, which would form the basis of his academic thesis that he submitted to become a docent.

In the short-lived coalition government of Bülent Ecevit that had been formed with the Islamist National Salvation Party led by Necmettin Erbakan, Baykal become the Minister of Finance.

Despite the government maintaining a small majority, the CHP lost ground in the Senate and by-elections held in October 1979, causing Ecevit to resign.

Like many politicians of the 1970s, Baykal was arrested and detained in Ankara, receiving a ban of five years from the military on grounds of political activities.

The newly formed Justice and Development Party (AKP), meanwhile, won a landslide majority in Parliament and put an end to years of unstable coalition governments.

Baykal was instrumental in assisting the AKP change the law in order to allow the party's banned leader, Recep Tayyip Erdoğan, to enter Parliament.

The CHP supported the change and Erdoğan was elected to Parliament in a by-election in 2003, subsequently taking over from Abdullah Gül as Prime Minister.

[2] Leading his party through the 2004 local elections, the CHP managed to increase their vote share but lost further ground, losing control of Antalya, Baykal's hometown, to the AKP.

As a result, the Mayor of Istanbul's Şişli district, Mustafa Sarıgül, challenged Baykal for the leadership in an extraordinary convention in January 2005.

Although Baykal won the election, the convention was marred by violence between supporters of the two opposing candidates, with Sarıgül being expelled from the party afterwards.

Baykal joined forces in an electoral alliance with the DSP in time for the 2007 general election, though the two parties combined only marginally improving on their 2002 result, winning 20.88% of the vote.

Due to the Nationalist Movement Party (MHP) surpassing the 10% threshold, the CHP's seats dropped considerably from 178 to 112.

In January 2009, Baykal criticized the establishing of TRT 6, which broadcast in the Kurdish language as he didn't see a benefit for Turkey if it only addressed the ethnic demands of a certain group.

This was due to criticism of his private life after an alleged video-tape showing him in the same bedroom with his former secretary, and a member of parliament Nesrin Baytok, was leaked to the media.

[5] He originally planned to run for the leadership again in the Ordinary Convention of 2010, since many members of the Central Executive Committee insisted that he retake his position as leader.

[6] Baykal was one of the five CHP politicians who were offered ministerial positions by Justice and Development Party leader Ahmet Davutoğlu in August 2015.

[11] He was buried in the Turkish State Cemetery in Ankara following the funeral service held at Ahmet Hamdi Akseki Mosque.