One of his main problems over that period has been that most people have not been entirely sure what that message is - something the Labour leader at least tried to address on the main stage in Brighton.
Amid the predictable Tory-bashing there were pledges-a-plenty, addressing issues including teacher recruitment and mental health.
He promised to turn Labour into a party the public could trust and insisted the country would have a strong economy under his leadership.
There was, however, another message – this one unspoken – that Sir Keir has been desperate to push through over the course of the conference.
Sir Keir wants us all to believe that Labour is now his party and that the Corbyn era is now well and truly over, but persuading people that this is true has proved to be no easy task.
Indeed, as he spoke, leaflets on some hideous sounding ideology called 'modern Corbynism' were selling like hotcakes outside the main hall at £4 a throw.
Since becoming leader Sir Keir has found it impossible to wash away the reek of the infamous Islington Trot, who appeared at the conference despite being suspended by the Parliamentary Labour Party.
And judging by the events of the past few days, it is questionable how many of those within the party are willing to join his attempt to turn his vision of becoming Prime Minister into reality.
To a great extent, Sir Keir's efforts to herald his new dawn have been overshadowed by the calamitous nature of everything that surrounds him.
An almighty inter-party row over rule changes was certainly not a good look for a leadership supposedly striving towards unity, and demonstrated that Labour remains obsessed with navel gazing instead of focusing on what is going on in the world outside.
One of his shadow cabinet threw in the towel, having claimed the party was more divided than ever under Sir Keir.
And then we had deputy leader Angela Rayner calling Tories 'scum'. While this no doubt delighted the few dozen activists present, it was hardly a sensible move if you want to win back some of the hundreds of thousands of former Labour voters who turned to the Conservatives at the last election.
There is also a clear detachment between the leadership and many party members over policy, as evidenced by delegates backing the nationalisation of the UK's energy industry and a £15-an-hour minimum wage, both of which Sir Keir is against.
Sir Keir insists that he can put Labour in a position to win a general election for the first time since 2005. He clearly realises the size of the challenge that faces him, and appears content to take baby steps in his drive for progress.
But as things stand, he is yet to convince many of those on his own side that he is an effective leader, let alone voters.
As the conference drew to a close rumours swirled around that Sir Keir's days may already be numbered, although looking at what is largely a motley crew assembled behind him, it is hard to see too many suitable candidates capable of doing a better job.
So the question must be asked, if not him, then who?