Brendan Cox, whose wife was killed by a right-wing extremist in June previous year, tweeted that PC Palmer is the "name I will remember" - not the suspect behind the horrific act of terror.
Palmer was a 48-year-old married father with 15 years of service, Rowley said.
Police officer Keith Palmer was killed in the Westminster attack.
The attacker had mowed down several pedestrians as he drove a grey Hyundai i40 across Westminster Bridge before crashing it into railings then running through the gates of the Palace of Westminster.
As further details emerge about the attack, the Metropolitan Police have confirmed that Constable Palmer was unarmed.
"He was someone who left for work today expecting to return home at the end of his shift and he had every right to expect that to happen", Rowley said.
British Conservative MP James Cleverly tweeted, "I've known Keith for 25 years".
Bystanders including lawmaker Tobias Ellwood (center) tried to save Palmer before he died..
Video: The Prime Minister is adamant that violence and terror is doomed after an attack in Westminster.
He said they'd served together in the Royal Artillery "before he became a copper".
Britain's allies reacted with shock and vowed to stand with London in the fight against terror, AFP says.
The fallen officer was mourned on social media as London began to come to grips with the attack.
Five South Koreans, three French youngsters on a school trip and two Romanians were also injured on the bridge, the woman rescued after falling into the Thames was rescued being urgently treated at the peir.
Press Association news agency photos believed to be of the attacker lying on an ambulance stretcher showed he was wearing black clothes and had a beard.