Getty ImagesPrimark boss Paul Marchant has resigned following an allegation by a woman about "his behaviour towards her in a social environment".
Associated British Foods (ABF), which owns Primark, said following an investigation by external lawyers, Mr Marchant "acknowledged his error of judgement and accepts that his actions fell below the standards expected" by the business.
Mr Marchant co-operated with the investigation and apologised to the individual, said ABF.
George Weston, chief executive of ABF, said: "I am immensely disappointed. Colleagues and others must be treated with respect and dignity. Our culture has to be, and is, bigger than any one individual."
He added: "At ABF, we believe that high standards of integrity are essential. Acting responsibly is the only way to build and manage a business over the long term."
The company said it remains in contact with the individual "who rightly raised her concerns and have offered her our support".
ABF's share price fell by nearly 4% to £18.64 each after the announcement.
Mr Marchant became chief executive of Primark in 2009. The retailer is known for its low-priced clothing and ubiquitous presence on the High Street.
Primark is a key part of the wider ABF business, contributing £9.4bn in sales in the last financial year out of the firm's overall revenues of £20bn.
Following Mr Marchant's "immediate" departure, ABF's finance director Eoin Tonge will become Primark's interim chief executive.
The firm's financial controller, Joana Edwards, will step into Mr Tonge's role. The company said: "Both executives have the experience to perform these roles well."
