The pedestrian crossing at the junction of Blackfriars Road, The Cut and Union Street is the first in the UK to be fitted with a countdown indicator showing walkers how long they have left to cross.
The screens have already been installed and will be switched on during the week of 21 June. The junction is right outside Transport for London's Palestra offices.
The new countdown screens are part of an 18-month trial by TfL at eight junctions across London. Two other SE1 locations will feature in the trial: the junction of Tower Bridge Road and Tooley Street and the crossing on Old Kent Road close to the Surrey Square junction.
Countdown timers are not currently permitted in the UK so TfL had to seek special permission from the Department for Transport and Highways Agency before launching the trial.
Pedestrian Countdown will replace the blackout period after the green man is switched off with an electronic signal showing exactly how many seconds remain to safely cross the road before the red man light comes on.
Research carried out last year showed that 60 per cent of pedestrians failed to understand the blackout period between the green light being extinguished and the red man being switched on.
In London the blackout is timed to allow a person stepping off the kerb just as the green light goes out sufficient time to complete their crossing.
TfL claims that Pedestrian Countdown will help pedestrians to feel safer by removing any uncertainty they may have when crossing and help to smooth traffic flow.
Mayor of London Boris Johnson has been talking about introducing Pedestrian Countdown for at least 18 months.
In 2008 he told the London Assembly: "I also think that if you look at the phasing of traffic lights, again, I think the countdown system will greatly help pedestrians and encourage them to have the confidence to cross the road.
"This is not a zero sum game. There are things you can do to smooth traffic and reduce frustration, reduce the irritation of people stalled in traffic without prejudicing the rights of vulnerable road users."