Poroshenko was born in the city of Bolhrad, in Odessa Oblast, on 26 September 1965 to Aleksei Ivanovich Poroshenko and Eugenia Sergeevna (née Grigorchuk). Little is known about his mother but a Ukrainian newspaper said she was an accountant, who taught at a vocational and technical school of accounting. He also spent his childhood and youth in Bendery (Moldavian SSR, now under de facto control of the unrecognised breakaway state Transnistria). where his Father Oleksiy was heading a machine building plant.

In 1984 Poroshenko married a medical student, Maryna Perevedentseva (born 1962). Their first son, Oleksiy, was born in 1985 (his three other children were born in 2000 and 2001).

From 1989 to 1992 Poroshenko was an assistant at the university's international economic relations department. While still a student, he founded a legal advisory firm mediating the negotiation of contracts in foreign trade, and then he undertook the negotiations himself, starting to supply cocoa beans to the Soviet chocolate industry in 1991. At the same time, he was deputy Director of the 'Republic' Union of Small Businesses and Entrepreneurs, and the CEO "Exchange House Ukraine".

A number of businesses were once part of the Ukrprominvest which Poroshenko headed in 1993–1998. The investment group was dissolved in April 2012. Poroshenko has stated that upon beginning his political activity he passed on his holdings to a trust fund.

Between 1996 and 1998, UkrPromInvest acquired control over several state-owned confectionery enterprises which were combined into the Roshen group in 1996, creating the largest confectionery Manufacturing operation in Ukraine. His Business success in the confectionery industry earned him the nickname "Chocolate King". Poroshenko's Business empire also includes several car and bus plants, Kuznya na Rybalskomu shipyard, the 5 Kanal television channel, as well as other businesses in Ukraine.

Poroshenko's brother, Mykhailo, older by eight years, died in a 1997 car accident under mysterious circumstances.

Poroshenko first won a seat in the Verkhovna Rada (the Ukrainian Parliament) in 1998 for the 12th single-mandate constituency. He was initially a member of the United Social Democratic Party of Ukraine (SDPU), the party loyal to President Leonid Kuchma at the time. Poroshenko left SDPU(o) in 2000 to create an independent left-of-center faction, naming it Solidarity. In 2001 Poroshenko was instrumental in creating the Party of Regions, also loyal to Kuchma, but Solidarity never completed the merger.

In December 2001 Poroshenko broke ranks with Kuchma supporters to become campaign chief of Viktor Yushchenko's Our Ukraine Bloc opposition faction. After parliamentary elections in March 2002 in which Our Ukraine won the biggest share of the popular vote and Poroshenko won a seat in parliament, Poroshenko served as head of the parliamentary budget committee, where he was accused of "misplacing 47 million hryvnias" (USD$8.9 million). As a consequence of Poroshenko's Our Ukraine Bloc membership tax inspectors launched an attack on his Business. Despite great difficulties, UkrPromInvest managed to survive until Yushchenko became President of Ukraine in 2005.

Poroshenko was considered a close confidant of Yushchenko, who is godfather to Poroshenko's daughters. Poroshenko was likely to have been the wealthiest oligarch among Yushchenko supporters, and was often named as one of the main financial backers of Our Ukraine and the Orange Revolution. After Yushchenko won the presidential elections in 2004, Poroshenko was appointed Secretary of the National Security and Defense Council.

In September 2005, highly publicized mutual allegations of corruption erupted between Poroshenko and Prime Minister Yulia Tymoshenko involving the privatizations of state-owned firms. Poroshenko, for Example, was accused of defending the interests of Viktor Pinchuk, who had acquired state firm Nikopol Ferroalloy for $80 million, independently valued at $1 billion. In response to the allegations, Yushchenko dismissed his entire cabinet of ministers, including Poroshenko and Tymoshenko. State prosecutors dismissed an abuse of power investigation against Poroshenko the following month, immediately after Yushchenko dismissed Svyatoslav Piskun, General Prosecutor of Ukraine. Piskun claimed that he was sacked because he refused to institute Criminal proceedings against Tymoshenko and refused to drop proceedings against Poroshenko.

In the March 2006 parliamentary election Poroshenko was re-elected to the Ukrainian parliament with the support of Our Ukraine electoral bloc. He chaired the parliamentary Committee on Finance and Banking. Allegedly, since Poroshenko claimed the post of Chairman of the Ukrainian Parliament for himself, the Socialist Party of Ukraine chose to be part of the Alliance of National Unity because it was promised that their party leader, Oleksandr Moroz, would be elected chairman if the coalition were formed. This left Poroshenko's Our Ukraine and their ally Yulia Tymoshenko Bloc out of the Government.

Poroshenko did not run in the September 2007 parliamentary election. Poroshenko started heading the Council of Ukraine's National Bank in February 2007. Between 1999 and 2012 he was a board member of the National Bank of Ukraine.

Ukrainian President Yushchenko nominated Poroshenko for Foreign Minister on 7 October 2009. Poroshenko was appointed by the Verkhovna Rada (Ukraine's parliament) on 9 October 2009. On 12 October 2009, President Yushchenko re-appointed Poroshenko to the National Security and Defense Council. Poroshenko supported Ukrainian NATO-membership. However, he also stated NATO membership should not be a goal in itself. Although Poroshenko was dismissed as foreign minister on 11 March 2010, President Viktor Yanukovych expressed hope for further cooperation with him.

Poroshenko returned to the Verkhovna Rada (parliament) after the 2012 Ukrainian parliamentary election after winning (with more than 70%) as an independent candidate in single-member district number 12 (first-past-the-post wins a parliamentary seat) located in Vinnytsia Oblast. He did not enter any faction in parliament and became member of the committee on European Integration. Poroshenko's Father Oleksiy did intend to take part in the elections too in single-member district number 16 (also located in Vinnytsia Oblast), but withdrew his candidacy for health reasons. In mid-February 2013, Poroshenko hinted he would run for Mayor of Kiev in the 2013 Kiev mayoral election.

One of the most expensive airplanes in the world – Falcon 7X – was rented to travel to the island. It cost $145 000.

Poroshenko has been married to Maryna since 1984. The couple have four children: Olexiy (born 1985), the twins Yevheniya and Oleksandra (born 2000) and Mykhaylo (born 2001). Olexiy was a representative in the regional parliament of Vinnytsia Oblast. In November 2014, he became People's Deputy of Ukraine. Maryna Poroshenko is a cardiologist, who does not take part in public life, apart from her participation in the activities of the Petro Poroshenko Charity Foundation. Poroshenko became a grandfather on the day of his presidential inauguration of 7 June 2014.

On 7 December 2015 Poroshenko had a meeting with U.S. Vice President Joe Biden in Kiev which discussed the Ukrainian-American cooperation.

In 2016, The Chocolate King, by Tom Ward, was published about Poroshenko and the complicated challenges in dealing with the Oligarchs, internal corruption, Vladimir Putin, and the U.S. presidential election.

On 26 July 2017, Renat Kuzmin, First Deputy Prosecutor, and former Deputy Head of the Office of the Prosecutor General of Ukraine published a ruling by the Pecherskyi District Court (in Kiev) that orders the Security Service of Ukraine (SBU) to investigate President Poroshenko for possible state treason under Article 111 of the Criminal Code of Ukraine.

On March 30, 2018 Poroshenko submitted income declaration. Poroshenko declared that he spent 1.3 and 1.4 mln UAH on his vacations – two times less than in “Skhemy” investigation.

President’s Administration did not provide answer in regard to journalists’ inquiry. However, the Administration confirmed that the vacation really took place. Information on dates and details was provided only later to the Ukrainian division of Russian information agency Interfax-Ukraine. In some time, the details on president’s vacation were Classified.