The boyband, who announced their spilt last October, performed a two-hour set in front of more than 80,000 fans at the city's Croke Park stadium.
Kian Egan told the crowd: "As this is the very last Westlife concert, the whole idea was to be able to get out here and see our fans one last time and celebrate 14 years."
Mark Feehily added: "For 14 years, Westlife fans have made our dreams come true. This show is dedicated to each and every one of you. Our fans mean so much. You have never stopped supporting us.
"Thanks so much. You're not just our fans, you are our friends and have been with us each step of the way."
The band - who have sold more than 44 million records around the world - played almost their entire back catalogue at the gig, according to The Sun.
All four members were said to be emotional as the crowd sang along to their hits.
"Last night was loud but this is unbelievable," said Shane Filan. "Tonight is the loudest, best crowd we have ever had."
Nicky Byrne also acknowledged the thousands of fans who were watching the gig live in cinemas around the world.
"To all of you, you didn't just make the dreams of four lads come true," he said. "Much more - only for all of you none of this is possible."
The band's former manager Louis Walsh also attended the concert and praised the group before the show started.
"I have never known a band like this in all my time in the business," he said. "I didn't want them to break up yet - but they all wanted to go out on a high. And I'll definitely be managing Shane in his solo career."
Filan and Feehily are both said to be pursuing solo careers following the split, whereas Byrne and Egan are looking to move into presenting.
"We will always be member[s] of Westlife but we won't be a band anymore," Filan told the audience.
He added: "Thank you. I'll never forget this. These are times that will live in our lives forever."
Watch Westlife talk about their last ever show below: