Boris Johnson’s wife Carrie said the shocking news of Sir David’s attack in Leigh-on-Sea on Friday was “absolutely devastating”.
Ms Johnson added: “He was hugely kind and good. An enormous animal lover and a true gent. This is so completely unjust. Thoughts are with his wife and their children.”
Brendan Cox, husband of the Labour MP Jo Cox who was murdered in 2016, said: “My thoughts and love are with David’s family. They are all that matter now.”
Former prime minister David Cameron said Sir David was “a kind and thoroughly decent man ... Words cannot adequately express the horror of what has happened today. Right now, my heart goes out to David’s family.”
Theresa May, Mr Johnson’s predecessor at No 10, said the death was “heart-breaking”, adding: “A decent man and respected parliamentarian, killed in his own community while carrying out his public duties. A tragic day for our democracy. My thoughts and prayers are with David’s family.”
Former PM Sir John Major also paid tribute to the popular MP. “This is truly heartbreaking news of a good and decent man who, for over 30 years, was a dedicated public servant. My heart goes out to his family.”
Health secretary Sajid Javid was among the cabinet members who expressed their shock and grief about the killing. “Devastated to learn of Sir David Amess’ murder,” he said.
Mr Javid added: “A great man, a great friend, and a great MP killed while fulfilling his democratic role. My heart goes out to Julia, his family, and all who loved him. Let us remember him and what he did with his life.”
Fellow minister Michael Gove said the news was “heartbreakingly sad”. He added: “He was a good and gentle man, he showed charity and compassion to all, his every word and act were marked by kindness.”
Foreign secretary Liz Truss said the campaigning MP was “a lovely, lovely man and a superb parliamentarian ... My thoughts are with all his family and friends”.
Education minister Nadhim Zahawi described him as “a champion for animal welfare, the less fortunate, and the people of Southend West. You will be missed by many”.
Sir David, 69, was one of Westminster’s longest-serving MPs and was known as a passionate campaigner for animal rights and a highly-respected presence on the Commons back benches.
The father-of-five was born in Plaistow, and first entered parliament in 1983 as MP for nearby Basildon – later moving to Southend West in 1997.
Labour leader Sir Keir Starmer said his thoughts were with Sir David’s family after the “horrific and deeply shocking news”, while former Labour PM Gordon Brown said he was “saddened and shocked” to hear about the death. “My condolences to his family and friends.”
Liberal Democrat leader Sir Ed Davey also mourned the “tragic news”, adding: “A truly terrible day for British politics but most importantly of all our prayers are with all the people who loved David.”
The SNP’s leader at Westminster Ian Blackford MP said he was devastated by the news. “Sir David was a thoroughly decent man, who was well liked across parties and the House of Commons … All of us are united in sadness today.”
Scotland’s first minister and SNP leader Nicola Sturgeon described it as “awful beyond words”, adding: “Elected representatives from across the political spectrum will be united in sadness and shock today.”
Flags were lowered to half-mast outside parliament following Sir David’s death, while Commons speaker Sir Lindsay Hoyle said he was “shocked and distressed” by his killing.
“David was a lovely man, devoted to his family, to parliament and his Southend West constituency,” said the Speaker. “He was well liked by members and the staff alike, and during his almost four decades here, built a reputation for kindness and generosity.”
Saying the killing would send “shockwaves across the parliamentary community”, Sir Lindsay added that Commons authorities will need to “discuss and examine” MPs’ security in the days ahead.
The MP for Southend West suffered multiple injuries on Friday at the Belfairs Methodist Church in Leigh-on-Sea. The MP was treated by emergency services workers after the arrival of an air ambulance but died at the scene.
Essex Police said a suspect is in custody and has been arrested on suspicion of murder. Officers are not looking for anyone else in connection with Sir David’s death.
Sir David is the second sitting MP to be killed in five years, following the deadly attack on Jo Cox in 2016.