Corbyn has won re-elections as Member of Parliament for Islington North seven times. In the 2015 election, when he won 60.24% of the votes cast and a majority of 21,194. During his career, he voted against the whip 428 times while Labour was in power.
In 1990, Corbyn almost went to jail for not paying his taxes as protest to a new tax system in Scotland.
In October 2001, Corbyn was elected to the steering committee of the Stop the War Coalition, which was formed to oppose the Afghanistan War which started later that year. He helped organise the February anti-Iraq War protest which was claimed to be the largest such protest in British political history. In 2006, Corbyn was one of 12 Labour MPs to support Plaid Cymru and the Scottish National Party's call for a parliamentary inquiry into the Iraq War. He was elected chair of the coalition in succession to Andrew Murray in September 2011, but resigned in September 2015.
Corbyn has always opposed weapons of mass destruction (WMD) and is a long-time supporter of the Campaign for Nuclear Disarmament (CND). He was criticised for inviting Gerry Adams and other members of Sinn Féin to the Palace of Westminster in 1984, weeks after the Brighton hotel bombing by the PIRA.
Corbyn was chair of the All-party parliamentary group (APPG) on the Chagos Islands, chair of the APPG on Mexico, Vice-Chair of the APPG on Latin America and vice-chair of the APPG on human rights. He has supported the rights for the Chagossians. He is known for his Venezuelan solidarity activism.
Following the Labour Party's defeat at the general election on 7 May 2015, Ed Miliband resigned as its party leader. His resignation caused the party to have a leadership election.
On 2 June, it was reported in media sources that Corbyn was thinking of applying to be a candidate. The next day, Corbyn announced to his local newspaper, "The Islington Tribune", that he would become a candidate in the election. Before he could become a candidate he had to secure at least 35 nominations from MPs. In the end he got 36. Some of the MPs who nominated him didn't think he would win and only nominated him to have a 'broader debate'.
Some, including former foreign secretary Margaret Becket, told journalists they regretted the decision. When he was accepted as a candidate Corbyn said: "This decision is in response to an overwhelming call by Labour Party members who want to see a broader range of candidates and a thorough debate about the future of the party. I am standing to give Labour Party members a voice in this debate". He would run against candidates Yvette Cooper, Andy Burnham and Liz Kendall.
Corbyn was elected party leader in a landslide victory on 12 September 2015 with 59.5% of first-preference votes in the first round of voting. It has been said that Corbyn would have won in the first round with 51% of votes. Corbyn's 40.5% majority was larger than that won by Tony Blair in 1994.
After being elected leader on 12 September 2015, Corbyn became Leader of the Official Opposition. On 14 September 2015, his seat in the Privy Council was announced. During his time as leader, Corbyn wanted to stop the "theatrical" nature of the House of Commons. His first months as leader was called as "a good start" and a "long overdue" change by "The Guardian". He made his first annual address as leader on 29 September 2015. As Leader of the Opposition, he was made a member of the Privy Council on 11 November 2015. The phrase, "Corbynmania", is used for the large amount of support given by his supporters.
On 16 June 2016, MP Jo Cox was assassinated after being stabbed multiple times by far-right supporter Thomas Mair. In the aftermath of the assassination, Corbyn described Cox as someone who was "dedicated to getting us to live up to our promises to support the developing world and strengthen human rights".
In June 2017, Corbyn made an appearance at the 2017 Glastonbury Festival, where he addressed the crowd. The crowd chanted "Oh, Jeremy Corbyn" and sang to the tune of "Seven Nation Army", a song by The White Stripes. Corbyn talked about the importance of young people going out and vote.
After members of ISIS carried out terrorist attacks in Paris in November 2015, Corbyn said that the only way to deal with the threat by ISIS would be to reach a political settlement and ending the Syrian Civil War. Corbyn voted against military power and airstrikes on ISIS.
In June 2016, Corbyn said he supported the United Kingdom staying in the European Union. After the United Kingdom voted on leaving the European Union, many Labour leaders wanted Corbyn to resign.
After the referendum, many members of Corbyn's Shadow cabinet resigned because they did not like Corbyn's leadership. Hilary Benn called Corbyn to tell him that he had "lost confidence" in his leadership. Corbyn later asked for his resignation from the Shadow Cabinet on 26 June. Heidi Alexander resigned from the Shadow Cabinet hours later, followed by Gloria de Piero, Ian Murray, Lilian Greenwood, Lucy Powell, Kerry McCarthy, Seema Malhotra, Vernon Coaker, Charlie Falconer, and Chris Bryant. Other Shadow Cabinet Ministers, including John McDonnell, Andy Burnham, Diane Abbott, Jon Trickett, Angela Smith, Emily Thornberry and Lord Bassam of Brighton have either supported Corbyn's leadership directly or have said that it was not a good time for a "rebellion". By mid-afternoon 27 June 2016, 23 of the 31 shadow cabinet members had resigned their roles as did seven parliamentary private secretaries.
On 28 June 2016, he lost the vote of confidence by Labour Party MPs by 172–40. He said with a statement that the motion had no "constitutional legitimacy" and that he intended to continue as the elected leader.
A YouGov poll of Labour party members found that about 50% expected to support Corbyn if a leadership ballot was called. London Mayor Sadiq Khan, who did not take a side in the dispute, said "When Labour splits, when we're divided, we lose elections". The division between Corbyn and the Labour parliamentary party continued.
On 11 July 2016, Angela Eagle announced her candidacy to run against Corbyn in the upcoming 2016 Labour Party leadership election. On 13 July former shadow minister Owen Smith also announced his leadership challenge. On the 19 July, Eagle quit the race after Smith got 90 nominations to her 70. Eagle said she resigned 'in the best interests of the party.' This was because having two anti Corbyn candidates in the race could split the vote and give him a better chance of winning.
On 24 September 2016, following the leadership contest, Corbyn was re-elected as the leader of the party again with an increased majority of 61.8%.
The Chilcot report of the Iraq Inquiry was issued on 6 July 2016. It criticised the former Labour PM Tony Blair for joining the United States in the war against Iraq. Corbyn was against the war in Iraq. In response, Corbyn apologised to the people of Iraq, families of British soldiers who died and to the British people.
After the election of Donald Trump in the 2016 United States presidential elections, Corbyn said that he believes that Trump is not solving problems, but dividing the United States. Corbyn also said he supports the idea for Trump to be banned from visiting the United Kingdom over his executive order on banning visitors from certain majority-Muslim countries from entering the United States.
In June 2019, Corbyn refused an invitation to attend a state banquet for Donald Trump, hosted by Queen Elizabeth II during the president's June visit to the United Kingdom. Corbyn then attended a London protest outside Trump and May's joint press conference and requested a meeting with Trump to talk about issues such as the "climate emergency, threats to peace and the refugee crisis". Trump rejected the request, saying that Corbyn was a "negative force".