The campaign's theme is '1,000 years of history...where history is still being written'.
Visitors will have the chance to attend a free talk about Big Ben by one of the clockmakers or guides, while people with children can take a themed family tour around Parliament.
In addition, rarely seen objects from Parliament's archives, such as the Ceremonial Silver Trowel used to lay the first stone of Big Ben, will be promoted on social media.
Amy Pitts, Parliament's head of visitor services and retail, said: "We are delighted to be participating in London History Day, especially as history is very much being written on this date during the pre-election period."
Today's activities are part of Historic England's 'Keep it London' campaign launched last year, in which the day when Big Ben first started keeping time – 31 May 1859 – came top in a poll to choose the date for London History Day.
The comms team at public body Historic England has been working with the Museum of London and the Greater London Authority to promote the awareness day.
More than 40 of the capital's museums and galleries are involved, and primary schools across the city are being encouraged to join in by allowing children to dress up as their favourite historic Londoner and using the event as a basis for learning.
Duncan Wilson, chief executive of Historic England, commented: "An awareness of our city's special character keeps us strong in times of change and throughout this day, we are encouraging people to look afresh at the stories and places that help define our city’s diverse and rich heritage."
And Sadiq Khan, London mayor, said: "London has been shaped by people from around the world for centuries who made this city their home.
"London History Day is a fantastic way for all Londoners to celebrate our city’s amazing heritage and open spirit, and to learn about how the capital has become the hotbed of culture, invention and creativity that it is today."
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