I have numerous examples of bigamous marriages in my tree, usually involving untruths on the part of one or the other party that they were widowed, or married again under their maiden name. Some later repeated the marriage when their circumstances changed to legalise it, for example when the previous husband who was already dead according to the information given at the first marriage (but was in reality still alive) had actually subsequently died, and the wife could claim to be a widow again, but that time truthfully.
One of my GGFs married 6 times, at least two of which were bigamous, and three of his wives had similar circumstances. And a GG Uncle who remarried bigamously after his first wife had left him, she in turn marrying again a further two times, firstly declaring herself a spinster, and then as a widow she later married the brother of her second husband which was itself illegal at the time.