How did Tony Blair become the prime minister of UK?

Tony Blair was elected leader of the Labour party in 1994 after the sudden death of the previous leader John Smith the Conservative Party had been in power for 15 years at that time and was very unpopular so it was highly likely that whoever won the leadership election would become Prime Minister in due course. This was the case and Labour won the General Election in May 1997 and Blair as their leader became Prime Minister.

It is alleged that there was a pact between Gordon Brown and Blair that Brown would not contest the leadership election in return for influence and on condition that Blair would eventually resign so that Brown could take over. This is sometimes called the Granita pact after the restaurant where the deal was allegedly made.