Turning to his own future, he vowed: ‘I take responsibility for not walking away, not plunging our country into chaos, as the Tories did time and again. Chaos that did lasting damage to this country.
‘A Labour government would never be forgiven for inflicting that on our country again.’
But he also warned party faithful: ‘For the British people, tired of a status quo that has failed them, change cannot come fast enough.
‘Truth be told, I am not sure they believe that we care. I am not sure they believe that we see their lives.’
He became solemn as he described his late brother Nick spent his adult life changing jobs and his sister’s work in a care home.
He continued: ‘I am fighting for them. We are fighting for them. I am their Prime Minister and this is their government.
‘I am the side of working people just like my sister.’
Sir Keir also pushed for closer ties with Brussels, saying he would put Britain ‘at the heart of Europe’.

He called Nigel Farage ‘a grifter’ and ‘a chancer’ for ‘taking Britain for a ride’ over the consequences of Brexit.
However, it is expected that the PM will stick to his so-called ‘red lines’ not to rejoin the single market or customs union.
Backbench Labour MP turned leadership threat Catherine West will decide whether to challenge Starmer after watching his speech.
She toldMetroshe would send an email to all her fellow MPs asking for their support if he did now she he was ‘fighting for working people’.
The Hornsey and Friern Barnet MP has made clear she wants a Cabinet member to come forward to challenge the Prime Minister.
There is speculation that her ‘stalking horse’ bid could help Health Secretary Wes Streeting run for the top job.

He has publicly supported the Prime Minister but there are reports he has told Sir Keir is preparing his case to take over.
Former deputy prime minister Angela Rayner, seen as another leadership rival, issued a statement last night telling her boss to ‘meet the moment and set out the change our country needs’.
She failed to explicitly endorse the PM or call for him to resign, but did say Greater Manchester mayor Andy Burnham should return to Parliament.
Burnham is viewed as a popular choice for the next Labour leader among many MPs but was blocked from trying to return as an MP by Labour’s national executive committee in January
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