Green’s Dictionary of Slang

an excl. of surprise, shock, wonder or amazement.

1894		S. Crane in N.Y. Press 20 May in Stallman (1966) 55: ‘Hully mack’rel,’ said Billie, ’I’ll never it t’ Omaha.’.
1907		‘Hugh McHugh’ Beat It 33: Holy mackerel! I’d like to see you travel over this part of the universe.
1914		G. Herriman Dingbat Family 24 Mar. [synd. cartoon strip] Merciful mackerel, wot’s this, wot’s this???
1919		H.C. Witwer Smile A Minute 300: ‘Holy Mackerel!’ says Frank, pale as milk, ‘it must of slipped outa my hand!’.
1921		N. Putnam West Broadway 219: ‘Holy mackerel!’ was what he said. And if you have been there you will know all that he meant.
1929		J. Lait Broadway Melody 40: Holy mack’rel — the biggest day o’ her young life, an’ she’s got the weeps.
1932		D.W. Lovelace King Kong 48: ‘Holy mackerel!’ he whispered. ‘Englehorn! Driscoll! Get a look at this thing’.
1938		W. Watson Miss Pettigrew Lives For A Day (2000) 115: Holy suffering mackerel! Where are we now?
1946		B. Cerf Anything For a Laugh 11: ‘Holy Mackerel,’ exclaimed the soldier.
1946		Wash Tubbs [synd. comic strip] Holy mackerel, Louie! We gotta stop that guy.
1953		T.A.G. Hungerford Riverslake 248: Holy mackerel, he’s in a hurry!
1956		I. Fleming Diamonds are Forever (1965) 163: Holy mackerel! Just any old dumb hag who can cook and lie on her back?
1959		E. De Roo Young Wolves 98: Holy Mackerel, that’s ambrosia!
1959		D. Niland Gold in the Streets (1966) 90: Holy mac, everything happens to me.
1960		‘Nino Culotta’ Cop This Lot 51: Joe looked very startled. ‘Holy mackerel,’ he said.
1965		R.L. Pike Mute Witness (1997) 43: Holy Mac, Lieutenant; what will Chalmers say?
1966		C. Stead Cotters’ England (1980) 76: Someone opened the front door. ‘Holy Mackerel, what time is it? Is that Nellie?’.
1969		‘Iceberg Slim’ Pimp 137: Holy mackul, boys. You smell dat?
1975		L. Rosten Dear ‘Herm’ 298: All I can say is Holy Mackeral.
1982		N. Keesing Lily on the Dustbin 24: Women used to let off steam domestically with a fine range of substitute expletives. ‘Holy Moses!’, ‘Holy mackerel!’, ‘great balls of fire’, ‘good gravy’, ’jumping Jehosaphat’ and ‘muddy great buckets of pitch’.
1996		Penguin Bk of More Aus. Jokes 382: Holy Mackerel, look at all them fucking Kooris!
2000		Indep. Rev. 2 May 7: Holy mackerel, he is going to pedestrianise the centre of London.