He has since been followed out of the door by at least eight other senior staff from Cabinet Office digital unit the Government Digital Service - including his respected deputy, Tom Loosemore.
Several sources told ComputerworldUK Bracken's departure was linked to civil service plans to "drastically" reduce the GDS budget and headcount as part of Whitehall spending cuts this autumn.
In recent days further sources have specified this will mean 100 GDS staff will leave before December, most of them currently working on 'Government as a Platform'.
It is an ambitious plan for common technology platforms and shared web-based infrastructure across departments to reduce duplication, save millions (if not billions) of pounds, improve public services and make them more consistent.
Once built, this would enable departments to share and reuse online platforms for different needs, for example for citizens to make payments to government (say, for a passport or licence) or track applications (for example for an environmental permit or Common Agricultural Policy payment).
It follows on from GDS's work to digitise 25 of the highest volume government transactions, building 15 by this year's March deadline.
The platform strategy was endorsed by civil service head Sir Jeremy Heywood last September and setting it up was GDS's main task post-election.
However, two weeks on since Bracken announced his exit, the future of Government as a Platform is in doubt, and the intrigue around GDS shows no sign of slowing.
Much of it has focused on civil service CEO John Manzoni, who arrived in Whitehall in October last year.
Sources say the former BP executive does not understand or support the digital reform agenda and rejected the case for Government as a Platform 'out of hand', not even allowing a business case for funding to go forward for consideration by HM Treasury.
Countless blog posts have been published by civil servants, some of them explaining their departure, others promising to stay, saying digital reform has barely even begun.
They can hardly be blamed to trying to maintain cheery optimism - many of them have spent years working on improving digital public services.
But it's far from clear they have the leadership from politicians and top civil servants they will need to continue reforms.
Senior leaders have scrambled to express support for GDS in recent days - including Cabinet Office minister Matthew Hancock, Chief Secretary to the Treasury Greg Hands and top mandarin Heywood.
However none have addressed the reports on plans to cut funding or abandon the 'GaaP' strategy.
Instead most have offered platitudes that they will take the "next leap forward", without specifying what that means in practice.
A Cabinet Office spokesman insisted that as the spending review is currently under way, "any talk of specific budgets is nothing more than speculation". He promised the department will build on Bracken's work "which will continue apace as planned".
However a number of those close to and inside GDS have privately expressed real concern in recent weeks.
"In my honest opinion, GDS is essentially done, unless people rally and bring a solution," one said.
"It's a problem of unaccountable, unelectable senior civil servants who run the world we live in and politicians not standing up to them. This is all about Manzoni cuddling up to departments and permanent secretaries," said another.
One ex-civil servant suggested the problem GDS has faced is that platform strategy is too vague.
"Do you understand what GaaP actually is What will be built/bought/delivered in reality Or perhaps articulate a vision of what Service X will look like in five years
"Imagine how it sounds to a spending review official in HM Treasury," he added.
This all leaves a crucial question: would Bracken have stayed if he felt digital reform plans, including Government as a Platform, had senior leaders' backing
One source close to Bracken told ComputerworldUK: "Number 10 were beside themselves [over his departure]. They wrote to [former Cabinet Office minister] Francis Maude to try to get him to come back. He said 'why would I, when you're not backing him'"
None of the new coterie of ministers or senior civil servants have publicly offered assurance they understand plans to transform digital services or can offer the strong political leadership needed to take them forward.
In a blog post, Hancock said he visited PwC yesterday with Hands to co-chair "a discussion on the power of digital to transform the entire public sector".
Several civil servants working in digital messaged ComputerworldUK with concerns about the meeting, given GDS's commitment to setting its own strategy rather than outsourcing it to external providers, and PwC's mixed track record in the public sector.
The Cabinet Office refused to release the notes or agenda from the meeting, who was in attendance or what was discussed when asked by ComputerworldUK.
It's understandable some conversations need to happen behind closed doors. But we need clarity on the future direction of digital reform in government - and, given the ongoing resignations of well-respected digital staff - we need it urgently.