In a Facebook message Mr Obama hailed the mother-of-two who volunteered for his 2008 presidential campaign for her work for those close to home in her Batley and Spen constituency and further afield.
He offered his condolences to her widower Brendan, son Cuillin and daughter Lejla, writing: “With our help, may they grow up in a world of greater tolerance, justice and peace - a future that would make their mum proud.”
He added: “Jo knew that our politics, at its best, still works - that, if we recognize our humanity in each other, we can advance the social justice, human dignity and peace that we seek in the world.
“Reflecting on a difficult time in university, she once said that it made her realize that it mattered where you were born, how you spoke and who you knew. In her radiant life, Jo turned that truth on its head.
“She was such an effective public servant for her beloved Yorkshire because she was born there. She earned the respect of her colleagues in Parliament because she was unafraid to speak her mind. And countless women, children and refugees around the world live with more dignity and hope because they knew Jo Cox and were touched by her work on their behalf.
“Today, we stand united - British, Americans and people around the world - to affirm that the hate and violence that took her from us are ultimately no match for the love and compassion that she spread in her life.”
• Thomas Mair, 52, from Birstall, has appeared at the Old Bailey charged with murdering Mrs Cox, grievous bodily harm against Mr Kenny, possession of a firearm with intent to commit an indictable offence and possession of a knife.