However, the National Security Council, which had been established following the 1980 military coup, banned İnönü from standing for office.

Standing down as chairman in order to be replaced by a politician that could seek office, İnönü was succeeded by Cezmi Kartay.

However, SODEP was banned completely from contesting the election, resulting in İnönü taking over as leader for a second time shortly afterwards.

Following the 1991 general election, the SHP formed a coalition with Süleyman Demirel's True Path Party (DYP) and İnönü became Deputy Prime Minister.

He graduated from the Physics Department of the Faculty of Sciences of Ankara University in 1947 and received his PhD from California Institute of Technology in 1951; with Eugene Wigner, he pioneered the study of group contractions.

[1] In 1974, İnönü moved to Boğaziçi University in Istanbul and lectured there until his venture into politics when he founded the Social Democracy Party (SODEP) in 1983.

Erdal İnönü was deputy prime minister in the two coalition governments formed between center-right DYP and SHP, which were led by Süleyman Demirel at first (from 1991 to 1993) and when Demirel became the president, by Tansu Çiller, in a unity largely caused by their resentment at the time against the outgoing Motherland Party.

Erdal İnönü died in Houston, Texas, United States, on 31 October 2007, where he was being treated for leukaemia.

[5] His body was flown to Turkey and was buried at the Zincirlikuyu Cemetery in Istanbul on 4 November 2007 following a state funeral held before the building of Turkish Grand National Assembly in Ankara the previous day and then an Islamic funeral in the Teşvikiye Mosque in Istanbul.