Aidan Brogan has resigned from his role as chief executive of Datalex with immediate effect.
Mr Brogan had occupied the position at the e-commerce company for almost seven years.
In a statement, Datalex said it would update the market in due course.
Deputy chairman Sean Corkery has been appointed as acting CEO while the board looks for a permanent replacement for Mr Brogan.
Earlier this year, accounting irregularities were identified following a review of the company's 2018 financial results.
An independent review by PwC later confirmed that Datalex's revenue, adjusted earnings and profit for the first half of last year were misstated.
It found that Datalex failed to adhere to the correct accounting standards and incorrectly recognised $3.5m (€3.1m) worth of services revenue in its accounts.
It also identified around $2.9m of other revenue that was incorrectly recognised in the period, of which around $700,000 is not recoverable.