Chelsea head coach Frank Lampard had said the 21-year-old was struggling with a minor unspecified problem in recent weeks, leading to his omission from the semifinal win over Manchester United.
Pulisic only featured as a substitute against Liverpool last week, and although he started Chelsea's final Premier League game against Wolves on Sunday, which ended in a 2-0 win, the winger was replaced 12 minutes from time as a precaution.
However, in an exclusive interview with ESPN, Pulisic said, "I never had a real issue. I'm 100% fit."
The news will come as a boost to Lampard and Chelsea, who are seeking their ninth FA Cup success and second big final victory over Arsenal in a year after beating them 4-1 in Baku to lift last season's Europa League trophy.
Pulisic had not yet signed for the Blues at that stage, but he said he had exchanged messages with former Borussia Dortmund teammate and Arsenal striker Pierre-Emerick Aubameyang, telling him "You can score one goal but you can't win!"
The pair remain close, with Aubameyang advising him on life in London prior to leaving Dortmund. But there has been no contact this time, as Pulisic singled out the Gabon international as a major threat after he amassed 27 goals in all competitions for the Gunners this term.
"I know him quite well," Pulisic added. "He is incredible, the way he gets in good areas. He's always dangerous, so we are definitely going to have to be cautious of that, and they have some other good players. But he is definitely one guy that you have to look out for.
"We'll always be good friends. I played together with him for a long time. Right now, we are definitely focused and want to win. It is going to be a good battle; and not so much on the pitch, but we will always be friends off the pitch.
"The final comes down to us against them, who is more ready to play on the day. Obviously, it gives us confidence that we've been in good form, we've been playing well, and we're going to try and bring that into the game. In the end, it is one game, and in a final, anything can happen."