He was born at Gregynog Hall in Tregynon, Montgomeryshire, a younger son of David Lloyd Blayney and his wife Elizabeth Jones.
He became a soldier, saw service in Spain and the Low Countries, and came to Ireland in 1598 with Robert Devereux, 2nd Earl of Essex.
That he became a very wealthy man is indicated by the fact that he could afford to give his daughter Anne £1200 as her dowry for her ill-fated marriage to Lord Balfour.
He married Anne, daughter of Adam Loftus, Archbishop of Dublin and Jane Purdon, as her third husband,[2] and had eight children: Henry, Sir Arthur Blayney (High Sheriff of Montgomeryshire), Anne Lady Balfour, Mary, Martha, Elizabeth, Lettice, and Jane, who married Sir James Moore.
The case caused such a scandal that it was referred to the arbitration of King James I, who ordered the parties to settle their differences without further dishonour to either family: his sympathies seem to have been with Anne, as he asked why she would accuse herself of adultery, unless she had been coerced.