There will be a period of silence lasting 30 seconds before the start of the elite men's race and the mass start.
Organisers are also encouraging runners to wear black ribbons and a separate campaign has been launched for runners to cross the line with their hands over their hearts to mark the events in Boston that left three people dead and 150 injured, many seriously.
The build-up to the London Marathon and the race itself will go ahead as originally planned after a review of security arrangements by police, local authorities and race organisers.
Security for London is expected to be beefed up, although exact details have yet to be announced.
The period of silence will be observed on all three London Marathon starts (red, blue and green) and will be signalled by a whistle at both the start and finish of the 30 seconds.
Race director Hugh Brasher said: "We want to show our support for our friends and colleagues in Boston at this difficult time for the global running community.
"We are determined to deliver an amazing event that will focus on one of the core pillars of the London Marathon, which is 'to have fun and provide some happiness and a sense of achievement in a troubled world'."
Organisers moved to reassure runners and spectators that their safety will be paramount at Sunday's race following the bombing at Tuesday's marathon in Boston.
London Marathon chief executive Nick Bitel said: "The support we have been offered by our stakeholders and the wider running community has been outstanding. We have the full support of the Metropolitan Police, the Mayor's office and other authorities.
"We want to reassure our runners, spectators, volunteers and everyone connected with the event, that we are doing everything to ensure their safety and that the Virgin London Marathon 2013 is an outstanding success."
A statement from the organisers said the registration and associated events will go ahead as originally scheduled with Paralympic champion David Weir opening registration on Wednesday morning.
The statement added: "We have reviewed and will continue to review our security arrangements with the Metropolitan Police and other authorities.
"We are being fully supported in all aspects of the event to safeguard our runners, spectators, volunteers and staff."
Paula Radcliffe, a former London Marathon champion and the women's marathon world record holder, admitted however that many people would feel uncomfortable at having family spectating near the finishing line.
Radcliffe has faith that those in charge of security on Sunday but she admits she would have doubts about bringing her own family were she in the field.
She told BBC Radio Five Live: "I have every confidence in the London Marathon community and the Metropolitan Police that they won't let it go ahead unless they have done everything possible.
"But it's still 26 miles...it's going to be hard. It's going to rely on people being vigilant and aware of what is going on around them as well.
"I think first and foremost as a mother I'd think more about having family at the finish area.
"You put yourself there at your own risk but putting family in that situation is something people are going to have to come to terms with and conquer."
Radcliffe said she felt sure competitors will want to take part.
She added: "It will raise so much emotion that people will want to stand up and show that it's not knocked the city of Boston down, not knocked marathoning down. If we can be sure it's safe and secure for other events to go ahead the vast majority will want to do that to help.
"It is a difficult situation. It seems very trivial to think about running a race when this has happened but on the other hand are you letting the terrorists win [by cancelling]?"
Sports minister Hugh Robertson said the Government was sure that safety could be maintained when asked if the London Marathon should go ahead.
He replied: "Yes, I do ... These are balance of judgments but we are absolutely confident here that we can keep the event safe and secure.
"I think this is one of those incidents where the best way to show solidarity with Boston is to continue and send a very clear message to those responsible."
Metropolitan Police commander Christine Jones said the public should be "reassured" the force was "very, very well-practised" at managing major events in London.
London mayor Boris Johnson said the police were taking extra security precautions for the race.