I swear blind?

[Homer55]

Where did this originate from?

[Quizmonster]

The earliest recorded use of the phrase 'swear blind' is from John Fowles' novel, The Collector, published in 1963.
The use of 'blind' in this way seems to be just a variant on other such emphasising phrases...eg 'He swore till he was blue in the face that he hadn't done it'. Similarly, the words 'Cor blimey!' is just a euphemistic alteration of 'God blind me!'

(Anyone convinced he was using the phrase in 1945 should present any written evidence of that to the editorial team at The Oxford English Dictionary.)

[Bert]

I would guess that the expression did not come into common usage as a result of its use in Fowles' book, but that it was in common verbal use long before that, as is hinted at in Quizmonster's challenge. I think that Quizmonster has hinted at the explanation of the meaning of the expression, but, just to make it explicit, I would suggest that "to swear blind" means to say "may God blind me if I am telling a lie".