The former Millwall striker has signed an 18-month deal at the Abbey.
He will take charge ahead of this Saturday’s game against Charlton Athletic.
Harris began his playing career at nearby Cambridge City, but he most notably played for and captained Millwall, where he achieved legend status by scoring 138 goals in 431 appearances, making him the Club’s all-time leading goal-scorer.
After retiring from playing in 2013, Harris coached the Millwall U21s before being handed the reigns to the First Team in 2015 on a permanent basis.
Whilst at the helm of the Lions, Harris won promotion from League One and led the Club to the FA Cup Quarter Finals, winning 42% of his 245 games in charge.
A move to Cardiff City followed, where he reached the Championship Play-Off semi-finals in his first full season in the job, before becoming Gillingham Manager in 2021, where he spent 20 months at Priestfield Stadium prior to leaving in October 2023, with the Club four points off top of the Sky Bet League Two table.
This is what the 46-year-old had to say about the appointment:
"I am super excited and really pleased to be here.
"It’s a brilliant project in motion here and I just want to come and add some value to that.
"I have seen the team evolve over the past four or five years and have always followed the results from my connections with the club from my younger days.
"I have always had an affinity with Cambridge but the players here have some brilliant attributes that suit the way I want to play.
"I want us to be a Cambridge United side that people fear playing against.
"I want to win games of football and address recent results as quickly as I can.
"It’s certainly not revolution, it’s about evolution and supporting the players that are already and trying to get a little more out of them."
Photo: Cambridge United
Majority Owner, Paul Barry, said he is confident that Harris can get the best out of the players.
He also felt Harris was exactly the right character for Cambridge United and is a strong cultural fit for where the club is at the moment.
Cambridge United sacked former Head Coach Mark Bonner last week, with the U's 18th in the League One table and without a league victory since October 2023.
Neil Harris will meet with the media on 7 December 2023 to further discuss his appointment to the role.