He was born in Zalău, but spent much of his childhood with his grandparents in nearby Pericei village, where he developed an interest in farming. After graduating from the agricultural high school in Șimleu Silvaniei in 1987, he attended the Faculty of Horticulture at the University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, earning a horticultural engineer's degree in 1994. He also holds degrees in the economy of agricultural development from the École nationale supérieure agronomique de Rennes and from the University of Montpellier 1, where he respectively earned a master's in 1997 and a doctorate in 2006. He has belonged to the agricultural think tank Groupe de Bruges since 2000. Although in Romania Cioloș is a political independent, he is affiliated with the European People's Party (EPP) at the European level.
From 1991 to 1996, Cioloș completed thirteen months' worth of internships on organic farms in the French region of Brittany. In the summer of 1995, he prepared a rural development project between Savoie and Argeș County, while working at the Aveyron agricultural chamber of commerce in Rodez during 1997, studying agricultural and rural development in the northern part of that department. In 1997 and 1999, he interned as an agro-economist at the European Commission's Directorate-General for Agriculture and Rural Development in Brussels, helping prepare the Special Accession Programme for Agriculture and Rural Development (SAPARD). In 1998-1999, he directed a local rural development programme in Argeș County, again cooperating with Savoie. From 1999 to 2001, he worked at two agricultural development agencies in France, coordinating joint programmes with Romania in that field. From 2002 to 2003, as part of the European Commission's delegation to Romania, he helped manage SAPARD's implementation in his native country. From January 2005 to May 2007, he was an adviser to Romania's Agriculture Minister, and a representative in the Council of the European Union's Special Committee on Agriculture. From May to October 2007, he was undersecretary of state for European affairs at the ministry. Following the resignation of Decebal Traian Remeș due to a corruption scandal, he was appointed Agriculture Minister in October 2007, serving until the following December, when Tăriceanu's National Liberal Party-led government left office after a parliamentary election. Early in 2009, he returned to work at the Agriculture and Rural Development DG, and that July, President Traian Băsescu named him to head a one-year commission looking at public agricultural development policies.
In October 2009, the Emil Boc government, hoping to secure the Agriculture portfolio in the second Barroso Commission, nominated Cioloș as Romania's EU Commissioner. The proposal was criticised by the opposition Liberals and Social Democrats, who saw it as a last-ditch maneuver by a government on the brink of collapse, as well as by the Party of European Socialists, who believed that the position ought to have gone to a Social Democrat. Boc's cabinet did indeed collapse the day after nominating Cioloș, when it lost a motion of no confidence.
At the end of November, Barroso nominated Cioloș to the Agriculture position, observing that he was the "most competent" of those submitted for consideration, and lauding his "modern vision" of agriculture and rural development. The British magazine Farmers Weekly considered the nomination "a controversial choice", citing recent mismanagement by Romania of EU funds, but also acknowledged his "broad agricultural experience". England and Wales' National Farmers Union as well as Scotland's NFU welcomed the appointment. Italian Minister of Agriculture Luca Zaia and French President Nicolas Sarkozy likewise congratulated Cioloș. German news agency Deutsche Presse-Agentur and British newspaper The Independent both criticised the nomination due to the funds mismanagement issue, with French daily Ouest-France alleging that the cause of British indignation was the perception that Cioloș would be akin to a second French EU Commissioner, given his close ties to that country.
After winning approval from the European Parliament in February 2010, Cioloş set forth his priority: maintaining a "thriving agricultural sector" in order to ensure food security, environmental preservation and protection of the countryside, help combat global warming and maintain a "fair standard of living" for farmers. As part of this objective, he promised to continue adapting and restructuring the Common Agricultural Policy.
In July 2015, Barroso's successor Jean-Claude Juncker named Cioloș as his special adviser on international food security.
In November 2015, Prime Minister Victor Ponta resigned following protests sparked by a deadly nightclub fire, and President Klaus Iohannis appointed Cioloș as his successor. The latter proposed a technocratic cabinet composed of twenty-one members, a third of them women. The cabinet won approval from Parliament on a 389–115 vote: the main Social Democrats and National Liberals were both in favor, although a number of legislators from the former party defied the leadership to vote against the cabinet. Additionally, the Alliance of Liberals and Democrats was opposed. He considers his two main achievements while in office to have been an increase in transparency, including the online release of salaries and expenditures for public institutions and financing contracts; and a reduction in bureaucracy that involved the elimination of numerous formalities. Ahead of the 2016 parliamentary election, Cioloș received the endorsement of the National Liberals and of the Save Romania Union, in turn urging voters to back either party. When these parties lost the election, the prime minister expressed his regret; the following month, he was succeeded by Sorin Grindeanu.
In 2000, Cioloș married Valérie Villemin, a French agriculture expert he met while studying in her country. The ceremony took place in his grandparents' village of Pericei. The couple have no children. He has a younger brother, Sorin. Cioloș is a member of the Romanian Orthodox Church.