Jeremy Corbyn has called on Labour to "come together" amid an angry backlash over his readmission to the party just weeks after he was suspended from it.
The former opposition leader said he was "pleased" to have been reinstated in the party and thanked "members, trade unionists and all who have offered solidarity".
He tweeted: "I am pleased to have been reinstated in the Labour Party and would like to thank party members, trade unionists and all who have offered solidarity.
"Our movement must now come together to oppose and defeat this deeply damaging Conservative government."
Mr Corbyn had the whip withdrawn and was suspended from the party last month over his response to a damning Equality and Human Rights Commission (EHRC) report which found that Labour had broken the law in its handling of anti-Semitism complaints.
He said the scale of anti-Semitism in the party was "dramatically overstated for political reasons" by opponents and "much of the media".
Mr Corbyn later sought to clarify the remarks, but his reinstatement has been met with fierce opposition.
Senior Labour MP Dame Margaret Hodge, who is Jewish, said she could not "comprehend" why it is acceptable for him to be a Labour MP "if he thinks anti-Semitism is exaggerated and a political attack".
She tweeted: "This is a broken outcome from a broken system. A factional, opaque and dysfunctional complaints process could never reach a fair conclusion. This is exactly why the EHRC instructed Labour to setup an independent process!"
The Board of Deputies of British Jews said the decision was a "retrograde step for the party in its relations with the Jewish community" and warned that "Labour's mountain to climb to win back the trust of our community just got higher".
While Gideon Falter, chief executive of the Campaign Against Antisemitism, said the lifting of Mr Corbyn's suspension showed "the Jewish community has been conned".
He said the "shambolic suspension and readmission" of Mr Corbyn appeared to have been "nothing more than a media stunt to blunt the blow" of the EHRC report.
"By readmitting Mr Corbyn, the Labour Party has once again excused anti-Semitism and proved itself unwilling to address it," he claimed.
The Jewish Labour Movement said it appeared Mr Corbyn's case had been "expedited" by a "factionally aligned political committee".
In a statement, the group said: "It is extraordinary that just weeks after the EHRC found that the Labour Party has discriminated against Jewish members through political manipulation of the disciplinary process, it appears that the party expedited this case for hearing by a factionally aligned political committee.
"After his failure of leadership to tackle anti-Semitism, so clearly set out in the EHRC's report, any reasonable and fair-minded observer would see Jeremy Corbyn's statement today as insincere and wholly inadequate."
Labour MP Neil Coyle, a prominent critic of Mr Corbyn, suggested the Equality and Human Rights Commission "may not be done" with the party in the wake of his readmittance.
And Conservative Party co-chairman Amanda Milling claimed that by allowing Mr Corbyn back, Labour is "sending a message that the shameful anti-Semitism of recent years should be allowed to continue".
However, Unite general secretary Len McCluskey, a close ally of Mr Corbyn, said the former leader's readmission was the "correct, fair and unifying decision".
"As a party we now move forward to implement the EHRC's recommendations and redouble our efforts to inspire voters about Keir's 10 pledges... and the transformation of our nations into fairer places for our people," he tweeted.
"Only Labour, united and strong, can bring this about."
Mr Corbyn had claimed that while "one anti-Semite is one too many" the "scale of the problem was also dramatically overstated for political reasons by our opponents inside and outside the party, as well as by much of the media".
He was suspended after his successor as Labour leader Sir Keir Starmer said that people who believed it was "exaggerated, or a factional attack" were "part of the problem" and "should be nowhere near the Labour Party either".
But Mr Corbyn acknowledged ahead of a meeting of the disputes committee on Tuesday that concerns around anti-Semitism in Labour were not "exaggerated".
He revealed he had given a statement to the party in an attempt to "clear up any confusion" over his initial response and a broadcast interview given in the wake of the report.