The former Crawley Town boss arrived at Fratton Park in December, but won just four of his 20 matches in charge - and none of his last six - to see the club plummet towards the League Two relegation zone.
Just four years after competing in the Premier League, Portsmouth are in danger of dropping out of the Football League altogether, currently lying 22nd in the division, just two points above Northampton Town in the drop zone.
"Following a meeting between Richie and the board, both parties agreed that it was in the best interests of the club," a statement on the club's official website confirmed.
"Portsmouth Football Club would like to thank Richie for all his work and wish him well for the future.
"Andy Awford has been appointed caretaker manager until the end of the season."
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