Green’s Dictionary of Slang

a mild, if once blasphemous oath, lit. ‘by God!’.

1696		G. Granville She-Gallants II i: He speaks like an Angel, beged [...] Men are as abominable Rogues as ever, always Drunk, and always Pox’d, begad.
1696		D. Manley Lost Lover III ii: Be-gad Madam! You don’t know what an Insipid Fellow I am this way.
1742		Fielding Joseph Andrews (1954) IV 319: ‘Begad, madam’ answered he, ‘’tis the very same I met.’.
1851		Thackeray A Plan for a Prize Novel in Burlesques (1903) 233: Begad, Snooks! I lick my lips at the very idea!
1862		Thackeray Adventures of Philip (1899) 100: She would be no more use in a sick-room than a – than a bull in a china-shop, begad!
1884		H. Smart Post to Finish III 184: Begad, if anything happens to her, hanging’s too good for you.
1890		Kipling ‘The God from the Machine’ in Soldiers Three (1907) 5: They called me Buck Mulvaney in thim days, an’, begad, I tuk a woman’s eye.
1903		J. Furphy Such is Life 36: ‘You don’t say so?’ ‘Fact, begad!’.
1913		‘J.W.L.’ Slave Stories 87: Begad, sir.
1922		Joyce Ulysses 122: So it was, begad, Ned Lambert agreed.
1925		L. Doyle Dear Ducks 273: Begad, I have a great notion.
1927		(con. 1835–40) P. Herring Bold Bendigo 41: First blood to Bendigo, begad!
1953		L. Doyle Back to Ballygullion 106: He’s a conceited, swelled-headed, self-satisfied pup, that thinks, begad, he knows everything.