Tomlinson 21, heartthrob to millions of teenaged girls around the world, has also been given squad number 28 which qualifies him to play for the club's first team in the second tier of English football, although that is unlikely to happen.
"This has always been a childhood dream for me," said Tomlinson, whose band are one of the biggest in the world and are preparing for a worldwide stadium tour starting next May.
A statement on the club's website (www.doncasterrovers.co.uk) said: "Louis has always been passionate about football and wanted to realise a dream of signing for his home town club where he once worked on match days."
He has also played at the club's Keepmoat Stadium in charity games and his signing for Doncaster is mainly to help raise funds for a local children's charity.
There are numerous links between the worlds of music and football but not many pop stars have signed for professional clubs.
Rod Stewart came close and had trials with London side Brentford before embarking on a full-time music career.
(Reporting by Mike Collett, editing by Amlan Chakraborty)
