Constantinescu was born in Tighina in 1939, where his parents were temporarily living. He received three degrees from the University of Bucharest: in law (1960), geology (1966), and a doctorate in geology and geography (1979). He practiced law in Pitești in 1961–1962, but switched his focus to geology after deciding that a legal career would involve too many compromises.

However, along with many other intellectuals, he joined the Romanian Communist Party (PCR) in 1965, hoping to foster change from within. Named a professor of geology and geography in Bucharest the following year, he later became the department's PCR cell leader for organization and propaganda. He taught geology until 1990, when he was named pro-rector of the university. He rose to the position of rector(president) in 1992, and held it until 1996.

Constantinescu first graduated from the Faculty of Law and then the Faculty of Geology and Geophysics of the University of Bucharest, and subsequently started a career as a Geologist. He has doctorates: in Geology from the University of Bucharest and Sciences from Duke University, USA. Beginning in 1966, Constantinescu taught in the Geology Department of the University of Bucharest.

After the Romanian revolution in 1989, Constantinescu became a founding member and vice President of the Civic Alliance. He was the acting chairman of the Romanian Anti-Totalitarian Forum, the first associative structure of the opposition in Romania, which was transformed into a centre-right political and electoral alliance known as the Romanian Democratic Convention (CDR).

The same year he was elected rector, he became CDR's candidate for President of Romania. He lost the election to then incumbent Ion Iliescu after the second round. In 1996, he competed once again for the presidency with the support of the Romanian Democratic Convention and managed to defeat Iliescu in the second round, securing a victory by a margin of roughly 10%. CDR's success at the 1996 general elections marked the first peaceful transition of power in post-1989 Romania. On the day he took office, he suspended his CDR membership, as the Constitution precludes a President holding formal membership of a political party during his tenure.

Nonetheless, throughout his four-year term, Constantinescu struggled with the slow implementation of the processes of modernization and privatization, which were bogged down by excessive bureaucracy. After another Mineriad which took place in 1999 and ended with the arrest of Miron Cozma, the remainder of his term suffered a political crisis between the majority parties that at the time formed the governing coalition. The country was further damaged by a drought in 2000. He voiced his support for autonomy in Székely Land, stating that not giving autonomy to the historical region would someday lead to a crusade of independence in the area. Eventually, his mandate ended with little short-term progress in economic privatization, as the state still controlled 80% of the economy.

A disenchanted Emil Constantinescu, who lost popularity and had failed to fulfill his reformist agenda announced on 17 July, 2000 that he would not run for a second term.. He temporarily withdrew from political life at the end of his term in November 2000. Constantinescu's direction in foreign affairs continued however after the comeback of Ion Iliescu in 2000. Eventually, Romania joined NATO in 2004.

The former President returned to the political scene in 2002 as head of the People's Action (Acţiunea Populară) party, which subsequently merged within the National Liberal Party in 2008.

Constantinescu has occasionally criticized the policies of the 2004–2009 President, Traian Băsescu, accusing him of authoritarian tendencies, and supported Crin Antonescu in the first round of the 2009 presidential elections.

A frequent speaker at the Oslo Freedom Forum, in 2010 he presented the OFF with a presidential medal. He is also a member of the international advisory council of the Victims of Communism Memorial Foundation.