The life of the party is the person who makes an occasion lively. He was the life of the party.
It always takes the, since the role is treated as singular. The British also say life and soul of the party, which is the fuller form.
1phraselife of the partyThe person who makes an occasion lively.
“She was the life of the party until about eleven.”
life of the party is a phrase.
Practised in Idioms