Another quote from the main site that it might be interesting to expand on. It seems to be first known in precisely that form in a novel by Frank E Smedley (full name Francis Edward Smedley) called Frank Fairleigh (1850).
But this is one of those quotations that evolved rather than being coined. Here's a historical survey:
1578: 'Anye impietie may lawfully be committed in love, which is lawlesse'. John Lyly Euphues.
1594: 'Deceit in love is but a merriment To such as seek a rival to prevent'. A Knacke to Knowe a Knave (anonymous play).
1606: 'An old saw hath bin, Faith's breach for love and kingdoms is no sin'. John Marston The Fawn.
1620: 'Love and warre are all one...It is lawfull to use sleights and stratagems to...attaine the wished end'. Shelton's translation of Don Quixote.
1801: 'In love and war, you know, all stratagems are allowable'. Maria Edgeworth Belinda.
1845: 'In love and war, every stratagem is fair, they say'. G P R James The Smuggler.
'You opened the letter!'...'How was I to read it if I hadn't? All's...fair in love and war, you know'.
But this is one of those quotations that evolved rather than being coined. Here's a historical survey:
1578: 'Anye impietie may lawfully be committed in love, which is lawlesse'. John Lyly Euphues.
1594: 'Deceit in love is but a merriment To such as seek a rival to prevent'. A Knacke to Knowe a Knave (anonymous play).
1606: 'An old saw hath bin, Faith's breach for love and kingdoms is no sin'. John Marston The Fawn.
1620: 'Love and warre are all one...It is lawfull to use sleights and stratagems to...attaine the wished end'. Shelton's translation of Don Quixote.
1801: 'In love and war, you know, all stratagems are allowable'. Maria Edgeworth Belinda.
1845: 'In love and war, every stratagem is fair, they say'. G P R James The Smuggler.