The 21-year-old singer has promised he and bandmates Harry Styles, Liam Payne and Louis Tomlinson will continue to be the "best" they possibly can in the wake of Zayn Malik's departure from the group, which was announced on Wednesday.
He tweeted: "Been a mad few days and your support has been incredible as per usual ! This in turn Spurs us on to make the best music we possibly can Put on great shows / tours for you guys.
"You are the best fans in the world and you deserve nothing less from us! (sic)"
And the 'Best Song Ever' hitmaker is already focused on the future and is looking forward to their upcoming concerts in South Africa.
He added: "The lads and I arrived in South Africa this morning . We cannot wait to see all you SA fans for the first time and have great shows (sic)"
Niall is the final member of the group to speak out following Zayn's decision to leave.
On Thursday, Louis thanked One Direction fans for helping him through a "crazy couple of days".
He wrote on Twitter: "Been a crazy couple of days but know that we are going to work harder than ever to deliver the best album we've ever made for you guys ! (sic)"
While he is still coming to terms with the devastating news, Louis admitted has been left delighted with the "truly incredible" support the fans, who are known as Directioners, have given the group.
He tweeted: "Your support has been incredible , truly incredible so thank you so much ! (sic)"
Harry also appeared to have taken Zayn's news hard yesterday as he broke down in tears during the group's first official gig as a four-piece in Jakarta, Indonesia, last night.
He later tweeted: "All the love as always. H (sic)"
Liam also took to Twitter to admit it had been a "strange 24 hours" after news of Zayn's decision broke.
He wrote: "So glad to be in bed after a long and strange 24 hours (sic)"