The former miner's son, Phil Kenny, 58, confirmed his father died on Monday morning.
Death of Bernard Kenny, hero who tried to save West Yorkshire MP Jo CoxRead more at: http://www.yorkshirepost.co.uk/news/death-of-bernard-kenny-hero-who-tried-to-save-west-yorkshire-mp-jo-cox-1-8703077
Mr Kenny, 79, was seriously injured when he was stabbed as he intervened when Thomas Mair attacked Mrs Cox in his home village of Birstall, West Yorkshire, in June 2016.
Her husband, Brendan Cox, tweeted on Tuesday: "Bernard Kenny was a hero, he personified the best of our country; risking his own safety to help others.
"Our thoughts & love are with his family."
Tracy Brabin, who was elected MP for Batley and Spen after the death of Mrs Cox, earlier told the Press Association: "My heartfelt condolences go out to Bernard's family at this sad time.
"I hope they will take comfort in the fact that Bernard will forever be remembered as a true hero, both as a member of the miners' rescue team and as a constituent of Batley and Spen who risked his life to protect Jo Cox.
"Bernard was brave and selfless, we will never forget him."
Mr Kenny was awarded the George Medal for his bravery this June, and said he was "honoured to receive such an award".
He was included in a list of bravery awards along with the two West Yorkshire Police officers who arrested Mair.
Pc Craig Nicholls and Pc Jonathan Wright both received the Queen's Gallantry Medal.
After Mrs Cox's murder there were numerous calls for Mr Kenny to be honoured, including a petition aimed at securing him the George Cross - the highest possible civilian honour.
At Mair's trial at the Old Bailey, the jury heard that the pensioner was waiting for his wife outside the library in Birstall when he saw Mair going "berserk".
He said in a statement to police: "I thought if I could jump on to the back, I could take him down.
"I thought he was thumping her until I saw the blood. I saw he had a knife in his hands. It was what I call a dagger. The blade was about nine inches.
"Just as I got short of him, he turned around and saw me. He shoved the knife in and it hit me in the stomach. The blood started pouring out between my fingers. I saw the blood and I thought 'Oh my God'."
Mr Kenny described Mair's actions as a "pure act of evil".
After the attack, more than 80,000 people signed an online petition calling for Mr Kenny to be awarded the George Cross for his bravery.
Mr Kenny, who shared a birthday with Mrs Cox, worked as a miner for 40 years and is a former member of the Gomersal Mines Rescue team which tried to save victims of the Lofthouse mine disaster in 1973.
Neo-Nazi Mair was given a whole life sentence for the murder of Mrs Cox, and was also found guilty of causing grievous bodily harm to Mr Kenny and possession of a gun and dagger.