The Swedish striker guided home a first-time finish following Jacob Murphy's knockdown eight minutes into the second half, to put the Magpies 2-0 ahead, before ultimately winning 2-1 at Wembley.
It is a first major trophy for Newcastle since an FA Cup triumph in 1955 and the 25-year-old understood how much it means to the club.
"It's fantastic. The club has been waiting for this for 70 years and it feels completely incredible," he told Viaplay after the match.
"It means everything. I've been in this club for a few years now, created relationships, and I think these players deserve this. And the supporters, they've been fantastic."
It could have been more for Isak - two minutes before his goal, he pounced on a rebound as Liverpool failed to clear a corner.
But his strike was ruled out as Bruno Guimaraes was in an offside position and stood in Reds' goalkeeper Caoimhin Kelleher's line of sight when the initial shot came in.
Speaking to Sky Sports, Isak discussed how he put the disappointment of the disallowed goal out of his mind.
"I think these games are about moments, and it's not necessarily about playing really good as a striker, it's about when you get the chance, to be ready, and to finish it off."
Now Newcastle have finally ended their trophy drought, the Solna native believes there is much more to come from the club and for its supporters.
"When you've been without a trophy for such a long time it can be in the back of your head, but hopefully now we've won this it can be bright days ahead of us."
"I think this is just the start. I think we'll see so much more."