The famous landmark will celebrate the arrival of the Duke and Duchess of Sussex's newborn by lighting up the night sky in the patriotic colours of the UK's Union flag.
Prince George, Princess Charlotte and Prince Louis's birth were all marked in the same way.
The BT Tower in central London will also scroll a message of congratulations for Harry and Meghan.
Tower Bridge - which acts on instructions from either Buckingham Palace or Downing Street - is often illuminated to celebrate high-profile royal births.
Royal babies are also usually commemorated with gun salutes in Green Park or Hyde Park and at the Tower of London.
But it is not yet known whether Harry and Meghan's youngster will be accorded the tradition.
The decision is in the Queen's gift, and Baby Sussex is only seventh in line to the throne and not an HRH.