Pompey will be massive underdogs for Saturday's final against Chelsea, who sealed the Premier League title with an emphatic 8-0 hammering of Wigan last Sunday.
The match represents a significant turn around in fortunes for former West Ham man Mullins, who thought he had blown his only chance of appearing in an FA Cup final when suspension ruled him out of the Hammers' final against Liverpool in 2006.
The 31-year-old admits he never thought he would be given a chance to make amends for the red card he picked up for clashing with Luis Garcia in a league game against the Reds three weeks before the final, which took place at Cardiff's Millennium Stadium.
The utility man is now relishing the prospect of playing against the Blues, and admits victory will mean more to him because the game is being played at the home of English football.
"Back in 2006 I got sent off against Liverpool and was given a three-game game ban," Mullins explained.
"That was a hard one to take but that was down to me and the other player from Liverpool. That was a bit stupid and a bit naive of me to be honest.
"To miss out on an FA Cup final was hard to take but now I'm back there with Portsmouth so hopefully I'll be able to play some part this weekend.
"I thought I'd missed my chance because the FA Cup final is such a a big game. It's so hard to reach a final because the top four are so strong but I'm there again now. It's at Wembley this time so it's a bit more special too."
Mullins has hailed the influence of Pompey boss Avram Grant, who has earned many plaudits by instilling a sense of unity within the Pompey camp despite the off-field problems which have dogged the club all season.
And having disposed of Champions League qualifiers Tottenham to make the final, Mullins is confident that the Israeli can upset his former employers this weekend.
"The manager has been great for the short period he's been here," said Mullins.
"He's been a brilliant manager, a great coach and a top motivator. And hopefully he will come up with a trick that can stifle Chelsea and that would be unbelievable.
"The boys are relaxed at the moment because there is no pressure on us," he continued.
"We know they are a great side and that they won 8-0 on Sunday. We know that they are champions, we know everything about them but we know that if we turn up relaxed on the day we might nick a win from a penalty or a free-kick like we did against Spurs."
A host of the club's top earners are expected to leave Fratton Park after this weekend's match, with the debt-ridden club keen to slash their wage bill as they head into the Coca-Cola Championship.
Portsmouth administrator Andrew Andronikou, who revealed last week that the club's debts now sit at £138million, will hold a meeting with the squad over their futures next week.
Mullins, who has two years left on his current deal, admits he does not want to leave Pompey despite their relegation to the second tier of English football.
"I have played there before a lot in my career, while I was at Palace and West Ham," said the Reading-born midfielder.
"It's a good club and hopefully if we get the right owner and the right people behind us then we can have stability and have a good go at it next year."