The human rights campaigner leading a Labour review into anti-Semitism in its ranks insisted she remained independent despite revealing she joined the party on the day she was appointed to the role.
Ex-Liberty director Shami Chakrabarti was brought in at the height of a row over alleged racist remarks that resulted in several high-profile figures being suspended, including MP Naz Shah and former London mayor Ken Livingstone.
Party leader Jeremy Corbyn, who faced allegations of not taking the situation sufficiently seriously, tasked her with helping set "boundaries of acceptable behaviour and language" and strengthening structures for dealing with racism of all forms.
He is due to present a promised beefed-up code of conduct to the party's National Executive Committee (NEC) tomorrow.
At a press conference to formally launch the inquiry, Ms Chakrabarti said she would investigate "without fear or favour" and produce recommendations that "will be mine alone".
Labour - along with other progressive parties - had to "openly look at itself in the mirror" and combat not only prejudice but also complacency, she told reporters.
But she stressed that she also wanted to be clear that she was "working for - and in the best interests of - the Labour Party" and that she had taken up membership because she "just wanted to be honest".
Asked if she felt it would undermine confidence that the inquiry - which she revealed would also have Labour peer Baroness Royall as a vice-chair alongside a leading Jewish academic - she said: "I consider myself to be independent.
"And I do not think I am less independent for making absolutely clear that I share the values of the Labour Party constitution and will seek to promote those values in any recommendations and findings.
"It is a judgment call but I thought that was the most honest thing to do - to be clear that I was undertaking this because I do believe in the values of the Labour Party and want to see them promoted not just in the Labour Party but in the world."
Ms Chakrabarti said she intended to seek evidence from Mr Corbyn as part of a process that will run until June 10 - with the final report due to be presented at the end of that month.
But she suggested it would be inappropriate to ask Mr Livingstone or other suspended individuals to take part while internal disciplinary investigations were ongoing.
She firmly rejected suggestions that the probe had been "diluted" by the extension of its remit to include Islamophobia and other forms of racism.
"There is no hiding from the fact the trigger for this inquiry was concerns about anti-Semitism. But anti-Semitism being a form of racism, it would seem odd to me to say the least not to look at all forms of racism including Islamophobia," she said.
Baroness Royall said that her investigation of alleged ant-Semitism in the Oxford University Labour Club was complete and a report will be presented to the NEC tomorrow and would be made public.
Ms Chakrabarti also said that she was satisfied the peer's fellow co-chair, Professor David Feldman, director of the Pears Institute for the Study of Anti-Semitism, did not have a conflict of interest.
Critics had pointed out that he is a supporter of a group of academics - Independent Jewish Voices (IJV) - which recently described allegations about Labour figures as "baseless and disingenuous".
Prof Feldman was asked about the statement at the press conference but she answered the query on his behalf, saying he had "distanced himself" from it.
"I am completely confident that he approaches this inquiry with an open mind, as do I," she told reporters.
She took a swipe at the Conservatives for failing to set-up a similar inquiry into complaints - including from senior figures such as ex-party chair Baroness Warsi - over the party's London mayoral campaign against Sadiq Khan.
"I'm not qualified to currently answer questions on the Warsi Inquiry into allegations of Islamophobia in the Conservative Party. Is there one? No, there isn't," she said.
"It is for other parties to look at their own. This inquiry and its findings intend to set the kind of standard that all democratic parties might seek to follow."
Asked if her decision to take up the role was related to Mr Corbyn being leader, she said: "I joined a Labour Party that has Jeremy Corbyn as its leader. Further, I joined the party on the day I accepted a chalice that may or may not contain water.
"That is all I want to say about that."