Pompey have appointed Danny Cowley as first team head coach on an initial deal until the end of the current season.
The 42-year-old former Lincoln and Huddersfield boss will be assisted by his younger brother Nicky.
Danny Cowley said: “This is a club with unbelievable tradition, so the board didn’t need to sell it to us. We’re proud and privileged to be here.
“Hopefully they saw two hard-working people who love the game and we’re delighted to be at Pompey.
“We always have the ambition of leaving a club in a better position than we found it. We’ll be doing everything in order to achieve that here.”
Pompey chief executive Mark Catlin added: “Having spent time with Danny and Nicky over the past few days – and speaking to those who know them well – I am delighted that we can finally announce their arrival at Fratton Park.
“We are all totally focused on giving Portsmouth Football Club the best chance of promotion in what is now, effectively, a 12-game mini-season.
“I would like to thank them both for the enthusiastic and professional way they have approached working with us for this period and there is an absolute collective desire to achieve success.”
Nicky Cowley said: “We’re looking forward to the challenge and this really is a great opportunity for us.
“The experience we’ve had in the game can hopefully stand us in good stead to have a strong finish to the season.”
After beginning his managerial career with stints at Concord Rangers and Braintree, Danny Cowley enjoyed great success in charge of Lincoln.
In his first season at the helm, he guided them to the National League title, with the side amassing 99 points.
The Imps also became the first non-league side to reach the quarter-finals of the FA Cup for 103 years during that 2016/17 campaign.
They did so by winning 1-0 at top-flight Burnley in the last 16, courtesy of a late goal by current Blues defender Sean Raggett.
Lincoln reached the League Two play-offs the following season – losing to Exeter over two legs – and then went up again as champions 12 months later.
Cowley departed for struggling Championship side Huddersfield in September 2019 and collected the division’s ‘Manager of the Month’ award in October.
He guided them to survival in the second tier, but left following a victory over promotion-chasing West Brom in the penultimate fixture.
Cowley spent his entire playing career in the non-league game and has a degree in physical education, previously working as a teacher at a school in Essex.
Brother Nicky has been his assistant at Concord, Braintree, Lincoln and Huddersfield, while the pair were also team-mates at Romford.
We are thrilled to have the Cowley brothers join the Pompey family. They have proved themselves to be fantastic managers of football clubs, and we feel fortunate to attract them to Portsmouth, a city that was a major reason why they came. #Pompey https://t.co/ldfUig1yo2
— Michael Eisner (@Michael_Eisner) March 19, 2021