The 26-year-old is currently plying his trade in Super Rugby with the Blues.
He often starts at centre, but will be able to provide competition for the No.10 shirt at Saints next season.
Jim Mallinder was keen to bolster his half-back ranks following the departure of JJ Hanrahan to Munster.
And Francis fits the bill, with the Gravesend-born back having built up a good reputation since arriving in Super Rugby.
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Francis headed to New Zealand to develop his game eight years ago and quickly gained experience in the National Provincial Championship for Auckland and Waikato.
After a short stint in Edinburgh, Francis was back in New Zealand, impressing for Tana Umaga at Counties Manukau.
That led to him being drafted into The Blues’ squad for 2016 and Francis’s play-making abilities in his 11 appearances earned him the rookie of the year honours for the Super Rugby outfit.
Later in the year he was at fly-half guiding Counties Manukau to a first win over Auckland at Eden Park in 39 years, en route to the Mitre 10 Cup semi-finals.
Francis has become a member of The Blues’ core squad and leadership group and has played in all four rounds of Super Rugby played to date.
And he is looking forward to the new challenge that will await him in England.
“I will always be thankful for my opportunities in New Zealand, and to Tana Umaga for giving me my chance with Counties Manukau and with The Blues,” Francis said.
“It’s been a brilliant time for me in Auckland, but I’m now excited by the prospect of joining the Saints and getting to grips with the Aviva Premiership.
“Northampton is a massive club that’s known the world over, and I’m joining a team with a huge amount of talent.
“It’s going to be brilliant to be training and playing alongside the calibre of players in the squad.
“I can’t wait to get started at Franklin’s Gardens, but before that there’s a lot of rugby still to be played in Super Rugby, and hopefully a game against the British and Irish Lions, too!”