The 23-year-old Irish star has as many as 30.9 million followers on the micro-blogging website, edging him past his bandmate, who has 30.8 million fans on Twitter.
However, the figures may not be a true reflection of their popularity, as Niall is notably more active on the social media platform than Harry, who is an infrequent tweeter.
And former One Direction star Zayn Malik trails all of the other lads, with a Twitter fanbase of 22.2 million.
However, the scene is quite different on Instagram, where Zayn leads the way with 23 million followers, while Niall has 19.5 million followers and Harry is on 21.2 million.
Liam and Louis are the least followed members of the group on the photo-sharing platform, where they have 13.7 million and 13.3 million followers respectively.
Despite his obvious popularity, Niall previously revealed he prefers to perform at intimate venues rather than huge arenas, as he has done during his One Direction days.
The singer-songwriter launched his solo career in 2016 and has admitted he relishes performing at a specific type of venue as a standalone artist.
He previously shared: ''My gigs are going to be a bit more intimate with minimal lighting; more of a gig than a show.''
What's more, Niall explained that his solo material wasn't suited to being performed at huge venues.
He said: ''I've been lucky enough to do the big shows with the big stages, the big lights and the big productions.
''For this type of music that I've been writing, I feel like bringing it down to me and the band.''
Here are all the performances from the comeback series of 'Twin Peaks'.
He's embarking on his first ever solo arena tour.
The singer has donated half a million to relief efforts.
Pratchett died aged 66 in March 2015.
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