Martin O'Neill stepped down as Ireland manager with a "heavy heart" on Wednesday after five years at the helm following a dismal run of results that resulted in relegation in the Nations League.

The former Celtic and Leicester boss, who replaced Giovanni Trapattoni in November 2013, left his post by mutual consent, with assistant manager Roy Keane also parting company with the Football Association of Ireland (FAI).

O'Neill guided his team to the last 16 at Euro 2016 and oversaw famous victories over Germany and Italy during his 55 games in charge. He also led the side to the playoffs for the 2018 World Cup in Russia.

"On behalf of the FAI board, I would like to thank Martin, Roy, and the management team for their work with the Republic of Ireland team over the last five years," said FAI president Donal Conway.

"Martin ensured that we enjoyed some great nights in the Aviva Stadium and on the road in Lille, Vienna, and Cardiff, which were fantastic high points for Irish football."

O'Neill said it had been an honour to be in charge of the team and paid special tribute to Keane, whom he described as "an inspirational figure in the world of football".

"It was one of my lifetime ambitions to take charge of the Irish senior squad and I would like to thank the FAI board for giving me that opportunity," he said in a statement released by the England-based League Managers Association.

"The Irish fans have been a source of motivation to myself, the team and the whole backroom staff, embodying the passionate Irish spirit, and I thank them for their fervent support of the team," he added.

"I am also very proud of the relationships I have built with the players, who have carried that very same spirit, imbued by the fans, onto the field of play."

Despite his achievements, O'Neill has endured a miserable run -- Ireland have won just one of their nine games in 2018, a victory against the United States in June.

The poor run of results culminated in a 0-0 draw against Denmark on Monday in Aarhus.

The side have also struggled for goals and have not found the net since September 11.

The FAI said its board would meet promptly to discuss the process of recruiting a new manager.