Aidan Brogan has resigned as Datalex's chief executive with immediate effect with his departure coming less than a week after the company's chairman said he would step down.
In a statement, Datalex said that Sean Corkery - its deputy chairman - will take up executive responsibility as acting CEO, while the Board undertakes a search for a permanent CEO.
The troubled airline e-commerce company said it will update the market in due course.
Mr Brogan has been beeen CEO at the company since September 2012 and first joined it in 1994.
Earlier this year accountancy irregularities were discovered in the company's 2018 interim accounts which had the effect of overstating earnings.
A forecast profit of $16m became an expected loss of up to $4m, before interest, tax depreciation and amortisation.
Datalex's Aidan Brogan steps down as CEO pic.twitter.com/3ttVnoi5e3— RTÉ Business (@RTEbusiness) May 2, 2019
Shares in Datalex have lost 62% of their value since the company issued that profit warning in the middle of January
Last week Datalex shareholders voted to accept a loan of €6m from businessman Dermot Desmond as its chairman Paschal Taggart said he would resign at the company's AGM in June.
"Somebody has got to fall on their sword in these situations, and I am the chairman, so it's me"," Mr Taggart had said at last week's EGM.
He added that at the age of 76 he had been planning to step down from the company for some time, and believed that new people coming in would add energy to the company.
He had declined to comment when asked if he thought there would be further resignations, particularly at executive level.
Meanwhile, Datalex temporarily suspended trading of its shares from May 1 as it failed to meet a regulatory deadline to publish its accounts, as scheduled, on April 30.
The Datalex share price has fallen substantially since the revelation of accountancy irregularities.
PwC was hired to conduct a review of its finances and it substantiated the claim that the company's finances had been misstated.
The review identified "significant accounting irregularities", which prompted the company to overhaul its finance function and implement improved controls.
Datalex said the review had identified significant accounting irregularities as the underlying cause for the group's overstatement of revenues, noting material weaknesses in the internal control environment.
It also disclosed that itss accounting process in this area has been largely manual, and dependent on individual judgement, and not subject to internal audit oversight.
The company's chief financial officer Dónal Rooney announced that he was leaving the company in February after just a couple of months in the role.