Sergey Stanishev has spent three decades at the centre of Bulgarian and European politics. He served as Prime Minister of Bulgaria from 2005 to 2009, led the Bulgarian Socialist Party for thirteen years and was President of the Party of European Socialists, the family of Europe's social democratic parties, from 2011 to 2022. Between 2014 and 2024 he represented Bulgaria as a Member of the European Parliament, sitting with the Progressive Alliance of Socialists and Democrats.

Having headed the Bulgarian Socialist Party's foreign policy and international relations department from 1996, Stanishev was elected party leader in December 2001 and held the post until 2014, a period in which the party won the 2005 parliamentary elections and returned to government. As Prime Minister of a coalition government from August 2005 to July 2009, he oversaw the final stage of Bulgaria's accession to the European Union, completed in 2007, during a period of strong economic growth. A member of the National Assembly from 2001, he chaired the parliamentary group of the Coalition for Bulgaria between 2009 and 2014.

At European level, Stanishev became interim President of the Party of European Socialists in November 2011, was elected President in 2012 and re-elected in 2015 and 2018, serving until 2022. In the European Parliament he was Vice-Chair of the Committee on Foreign Affairs, worked on the Committee on Economic and Monetary Affairs and served on the delegation to the EU–North Macedonia Joint Parliamentary Committee. A consistent advocate of Bulgaria and Romania's accession to the Schengen area, he served as the Parliament's rapporteur on the file, and full accession was completed in January 2025.

Stanishev graduated in history from Moscow State University in 1989 and received his doctorate in history there in 1994. He later specialised in political science at the Moscow School of Political Studies and was a visiting fellow in international relations at the London School of Economics and Political Science. A journalist before entering politics, he speaks English and Russian in addition to Bulgarian, and remains engaged in European policy debates through the Foundation for European Progressive Studies.