The recommendations for preventing future deaths made by the 7/7 coroner are "clear and welcome" and must now be considered by the relevant agencies, former London mayor Ken Livingstone said.
Mr Livingstone, who was mayor at the time of the attacks, described the suicide bombings as "a criminal act on a horrific scale".
He said: "July 7 2005 was the worst terrorist attack in London's history, an act of mass indiscriminate murder aimed at Londoners regardless of creed, colour or background.
"The choice of target - the transport system that holds London together - could not have been a more direct attack on Londoners.
"I welcome the unlawful killing verdict, a symbolic moment that records that this was a criminal act on a horrific scale.
"There are bound to be lessons from such a shocking event but what is clear is that emergency service staff responded with great efficiency and dedication."
He added: "The coroner's verdict includes a clear and welcome set of recommendations that the relevant agencies must now consider."
Boris Johnson, Mr Livingstone's successor as London mayor, said: "I am grateful to Lady Justice Hallett for this detailed, thorough and very sensible report.
"We will look carefully at her recommendations and I would like to reassure all Londoners and visitors to our great capital that much has changed in our emergency protocols, procedures and equipment since that day.
"Today is primarily a day of remembrance for those who tragically lost their lives, and for the many hundreds who were injured."
Home Secretary Theresa May said: "I am pleased that the coroner has made clear there is simply no evidence that the Security Service knew of, and therefore failed to prevent, the bombings on 7/7.
"The Government, emergency responders and the security and intelligence community are always looking to learn lessons and to improve the response to the terrorist threat we face.
"This includes learning from the July 7 attacks and from other incidents and there have been a considerable number of improvements put in place since 2005."
She added: "No one will forget the tragic events of that day and nothing will ever be able to bring back the 52 people who were murdered.
"But I do hope that the conclusion of the inquests will bring some measure of comfort to the families and all of those affected.
"This process has been vitally important. We now have a better picture of what happened in the lead-up to that terrible day and on the day itself. I and my Government colleagues will now carefully consider the coroner's report and recommendations."
Mrs May went on: "I would like to thank the police and Security Service for their continuing efforts to keep the public safe, and also the emergency services and everyone who helped the injured on that terrible day.
"They work day in and day out to protect the public and I value their important work enormously.
"Unfortunately, it is not possible to provide a risk-free world and we cannot guarantee that terrorists will never succeed. We must remain vigilant."
City of London Police assistant commissioner Frank Armstrong said: "Today our thoughts are very much with the families and friends of the victims who lost their lives on that tragic day on July 7 2005.
"Our thoughts are also with the survivors, who had horrific injuries and still suffer.
"We will now consider Lady Justice Hallett's report and recommendations in detail, and where necessary look to adopt all the improvements recommended.
"We should also remember the police officers and members of the public who displayed considerable bravery.
"I am incredibly proud of the City of London Police officers and staff, along with members of the public who went to assist at Aldgate Tube station on that day.
"We should remember all their efforts. They did their very best."