Originally launched in the UK in 1964 by the International Publishing Corporation, The Sun was originally aimed at a socially radical middle class readership but struggled to find that audience and by 1969 the paper was losing £UK2m each year. When IPC decided to sell off the title in 1969, it was acquired by Australian newspaper magnate, Rupert Murdoch, who had made his first major UK acquisition - The News of the World - the previous year. Since the News of the World was only published on Sundays, The Sun offered an opportunity to keep Murdoch’s presses running throughout the week. Both papers would be subsequently be run as sister publications, printed on the same presses and sharing senior management.

The post-Murdoch relaunched Sun was unrecognisable from its predecessor: adopting the tabloid first, the paper’d editorial was overtly populist, not to say sensationalist, a tone most overtly expressed by the introduction of the “Page Three Girl” (a topless model) from 1970 onwards. Though initially left-leaning (apparently reflecting owner Murdoch’s then political leanings) it began to move to the right in the mid-1970s and endorsed a vote for Margaret Thatcher’s Conservative party in the 1979 election.

The Sun was first sold in Ireland from May 1976 following an expensive launch campaign. Sales briefly climbed to 28,000 before settling at around 20,000. However, just four months later the paper withdrew from the IRish market, citing difficulties negotiating with the unions representing the printing staff tasked with producing additional copies for the Irish market.

The paper was relaunched in February 1986, on an initial print run of 50,000. The Irish edition was essentially identical to the UK version, although advertising for contraception (the sale of which was still largely prohibited in Ireland) and UK football betting pools were removed.

By 1987 the Sun was selling 23,000 - 25,000 a day in the Republic (although this was well behind sales of the rival Daily Mirror which sold 65,000 - 70,000 in Ireland). It was also dwarfed by sales of The Sun in Northern Ireland where, despite a much smaller population (one quarter that of the Republic), The Sun sold 85,000 copies a day).

The Irish Sun was launched in 1992 (at which stage the paper was still selling 23,000 copies a day). By the end of 1996 this had leapt to nearly 90,000 a day. 

Although retaining the same tabloid format and mode of address, the Irish edition of the Sun often adopted a very different editorial stance to the UK edition, one shaped by local politics. For example, in 2002, the overtly Euro-sceptic UK edition of The Sun described the introduction of Euro in 2002 as a huge error, while the Irish edition adopted a largely neutral approach.

In 2012, the paper effectively became a seven day operation following the closure of The News of the World as a result of reputational damage suffered by the latter following revelations about its use of illegal surveillance. At its 2007 peak the Irish News of the World had sold 154,000 copies each Sunday and was still selling over 120,000 weekly at the time of its closure. Established in the context of a universal decline in print sales, The Irish Sun on Sunday would struggle to match these figures. Sales dropped from 64,000 in 2012 to 45,000 by 2019 and 29,000 by mid-2023.

As for the daily edition, Irish sales would peak in late 2007 at 107,000 copies a day. Following the 2008 financial crash, and in line with the rest of the print publishing sector, sales declined, albeit at a faster pace than almost any other paper (with the exception of the Irish Daily Star). By 2015, sales had halved to 57,000 though they would plateau at around this level until 2018 when they began to fall again. ABC figures for mid 2023 suggest that circulation now hovers around 31,000.