Lakhvinder Cheema, 39, died hours after eating a leftover curry which had been in the fridge of his home in west London while his fiancee Gurjeet Choongh, 21, was violently ill.
The Old Bailey heard Lakhvir Singh, 45, had poisoned the food with Indian aconite.
Aconite, known as the Queen of Poisons, is one of the most deadly poisons but this was the first case in England since 1882, the Press Association reported.
Singh, also from west London, was found guilty at the Old Bailey of murdering Cheema in January last year and causing grievous bodily harm with intent to Choongh. She was found not guilty of attempting to murder Choongh.
After her arrest, Singh, a mother of three, tried to blame her brother-in-law for the death. But a lodger at the house saw her take a container with the curry out of the fridge earlier in the day, the court heard.
“Perhaps jealousy, anger and revenge all playing their part, Lakhvir Singh decided to poison them using an extremely toxic and deadly poison,” said prosecutor Edward Brown.
