The Prime Minister joined London Mayor Sadiq Khan and Metropolitan Police Commissioner Cressida Dick in a remembrance service a year on from the atrocity which left eight innocent people dead.
Victims’ families and friends laid flowers near the scene as the names of the dead were read out.
Crowds, including members of the emergency services, then fell silent to remember those killed and injured when a terrorist trio drove a van into pedestrians on London Bridge, before stabbing revellers in the nearby Borough Market with 12-inch ceramic knives.
Khuram Butt, 27, Rachid Redouane, 30, and Youssef Zaghba, 22, were shot dead by police just eight minutes after the first emergency call was made.
At Southwark Needle, close to the scenes of the atrocity, those injured and the dignitaries, who included Labour leader Jeremy Corbyn and Home Secretary Sajid Javid, were invited to lay flowers.
A floral wreath from Mrs May laid at the Southwark Needle read: “We will never forget those who died and will never surrender to hatred and division.”
Mr Khan’s tribute read: “Our city will never forget you. We stand united against terrorism and together in remembering the innocent lives lost.”
A service of commemoration was held at Southwark Cathedral earlier on Saturday, where Dean Andrew Nunn told the congregation: “I hope it helps our healing.
“Whatever your hopes are, whatever your pain is, whatever has kept you awake at night, whatever anger, sorrow or guilt you are feeling: God is here for you.
“Love is stronger than hate, light is stronger than darkness and life is stronger than death.
“It was true a year ago. It is as true today.”
Family members of those who died lit candles in memory of their loved ones and the 700-strong congregation held a minute’s silence.
Outside the cathedral, following the service, an olive tree - known as the Tree of Healing - was planted in the cathedral grounds using compost from floral tributes left on the bridge in the aftermath of the murders last year.
Ahead of the day’s commemorative events, the Prime Minister recalled the “stories of courage” which emerged from the attack.
She described it as a “cowardly attempt to strike at the heart of our freedoms by deliberately targeting people enjoying their Saturday night with friends and family”.
Mrs May said: “Today we remember those who died and the many more who were injured, and also pay tribute to the bravery of our emergency services and those who intervened or came to the aid of others.
“The many stories of courage demonstrated that night will always stay with me - such as Ignacio Echeverria, who died after confronting the terrorists with the only thing he had, his skateboard, and Geoff Ho, who spent almost two weeks in hospital after being stabbed in the neck as he shielded his friends.”
Those killed in the attack were Canadian Christine Archibald, 30, James McMullan, 32, from Hackney, Frenchmen Alexandre Pigeard, 26, Sebastien Belanger, 36 and Xavier Thomas, 45, Australians Kirsty Boden, 28 and Sara Zelenak 21, and Spaniard Mr Echeverria, 39.
Mrs May said the range of nationalities was “a reflection of our great cosmopolitan capital, whose energy and values brings together people from across the world, and a tragic reminder that the threat from terrorism transcends borders and impacts us all”.
She added: “My message to those who seek to target our way of life or try to divide us is clear - our resolve to stand firm and overcome this threat together has never been stronger.”
Mr Khan said the city would honour the victims of terror attacks “through our actions and standing united against terrorism and in hope for the future”.
He said: “Our city faced some incredibly difficult times last year, with the terrorist attacks in Westminster, London Bridge, Finsbury Park and Parsons Green.
“The cowardly terrorists who commit these horrific acts do so to try to divide us, to fuel fear and to change how we treat one another. I’m proud of the way we have responded: standing united in defiance and staying true to our values and way of life.”
Mr Nunn said the Tree of Healing will be “a constant reminder to us all of those who were harmed but also of the importance of our communities coming together to stand against violence in all its forms”.
A digital book of hope was available at Southwark Cathedral throughout the weekend for the public to sign.