Eoghan mac Eoinn (Anglicized: Ewen son of John), lord of Latharna (Lorne, Scotland) (born in est the 1330s, d before 1388) was a 14th-century Scottish Highland magnate.
Eoghan was the grandson of Ailean mac Eoin, a cadet of the exiled House of Ergadia (the senior line descending from Somerled) who was in English service in the 1320s, and son of Eoin mac Ailein, known as 'Gallda' ("the Foreigner") who styled himself 'Lord of Argyll', who made a return to Scotland, to claim or hold some of their ancestral estates.
It is not known whether it was his father, or only Eoghan himself, who made a reconciliation with the kings of the Bruce dynasty, but in mid-14th century, such a reconciliation occurred.
There are records which show that their family, in the 1350s, also made some agreement with their agnatic kinsman, the Lord of the Isles, whose lineage (a junior branch of the Somerled heirs) had received a lot of the old Ergadia-family lands from the victorious Bruce.
Eoghan married Janet Isaac, a granddaughter of Robert the Bruce, which signals of a reconciliation, even some favor, from the king David II, heir of the Bruce, and uncle of Janet.
In 1357 Eoghan had a grant of all the lands that had belonged to his great-great-grandfather Alasdair of Latharna (Alexander de Lorne) in Lorne.
Between 1365 and 1369, Eoghan is recorded as having attended Councils and Parliaments of Scotland.
It seems Eoghan did not have surviving sons.
His heiresses were two daughters, Siobhan (Janet) and Iseabail (Isabel), who married a couple of brothers from the Stewarts of Innermeath family.