Jennie Formby’s departure is the clearest sign yet that Labour is under new management.
The party’s general secretary was a key ally of Jeremy Corbyn – and of the leader of the Unite union, Len McCluskey.
Ms Formby’s supporters maintain that she oversaw swifter and stronger action in tackling allegations of anti-Semitism.
But her detractors accused her of not being robust enough.
She underwent chemotherapy for breast cancer last year but she has made no suggestion that she was resigning for health reasons.
Supporters of Labour’s recently-elected leader, Sir Keir Starmer, had wanted a new general secretary in place.
When Jeremy Corbyn first became leader in 2015, the then general secretary Iain, now Lord, McNicol had been appointed under the previous leadership – and there were widely reported tensions between the new leader’s office and party HQ.
Keir Starmer’s team did not want this repeated – but it is difficult to force out an incumbent who is determined not to go.
Change at the top
So before Ms Formby’s intentions became known, one of Sir Keir’s supporters said privately that an inquiry into the leaking of an internal document – which contained confidential staff messages – could provide the mechanism for removing her.
The general secretary is appointed by the party’s National Executive Committee (NEC) and following recent elections to the ruling body, Keir Starmer’s backers have a narrow majority.
They were keen that Jennie Formby should be replaced before further elections to the NEC take place later this year, in case their slender advantage is lost.
It had been assumed Ms Formby would have stood down ahead of the party conference in September.
This would have been after the inquiry in to the leaked document reports in July.
And it would probably have been after the Equality and Human Rights Commission delivers the results of its investigation in to anti-Semitism in the party.
But Ms Formby has instead chosen to go sooner, on her own terms, without awaiting the verdict of these probes.
Already, her possible replacements are being talked about in Labour circles.
One potential candidate is Lisa Johnson, a senior official at the GMB union.
She is on the left of the party but her union never toed the Corbyn leadership line.
However, the GMB is in turmoil following the departure of its general secretary Tim Roache – and the launch of an internal investigation in to serious allegations about his conduct in office.
Another possible candidate – thought to be favoured by some in Starmer’s inner circle – is Annaliese Midgley.
Although, like Jennie Formby, her background is in the Unite union, she is seen as someone who would be loyal to the new leadership.
The field could broaden.
But the significance of today’s resignation is that it should help Sir Keir Starmer in his mission to have the party HQ and the Labour leader’s office working in harmony.