The ceremony in Westminster Hall was held to mark the first anniversary of the attack and was attended by politicians, senior police officers and people involved in the incident.
Five people were killed, including Pc Keith Palmer, and dozens of others were injured when 52-year-old Khalid Masood launched a car and knife attack on Westminster Bridge and the Palace of Westminster before he was shot dead.
The Archbishop of Canterbury, Justin Welby, told the gathering: "A year ago, darkness struck across Westminster Bridge and in this palace.
"It spread across the bridge like a snake, driving to left and right, killing and harming."
Reverend Rose Hudson-Wilkin, the Speaker's chaplain, told the service: "A year ago today on this estate and on Westminster Bridge we were visited by what I regard as evil."
Rev Hudson-Wilkin praised Pc Palmer, saying he "ran towards the danger in order that we might be safe".
The vigil included a two-minute silence for the victims of the attack.
Masood's rampage left five people dead - 48-year-old Pc Palmer, who was on duty at the Palace of Westminster, along with US tourist Kurt Cochran, Romanian tourist Andreea Cristea, 31, and Britons Aysha Frade, 44, and 75-year-old Leslie Rhodes, who were mown down on the bridge.
Prime Minister Theresa May was not at the Westminster Hall service because she was attending an EU summit in Brussels.
But Downing Street said she had attended an earlier private service in the Chapel of St Mary Undercroft in the Palace of Westminster.
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