The first Night Tubes will roll on to London Underground platforms past midnight on Friday – almost three years since the plan was first announced.
Trains will run on the Victoria and Central lines on Fridays and Saturdays.
The plan was announced in November 2013 and intended to begin in September 2015, but strikes over pay delayed the start by nearly another year.
Transport for London said there was a “huge demand” as passenger numbers on weekends had soared by 70% since 2000.
Night Tube services are expected to add £6.4bn to the London economy by 2030, creating 500,000 jobs, TfL said.
Trains will run every 10 minutes on the full Victoria line and on the Central line between White City and Leytonstone. They will run approximately every 20 minutes between Ealing Broadway and White City and between Leytonstone and Loughton/Hainault.
Unions staged a series of strikes during July and August last year before an agreement was finally reached in March 2016.
Before leaving office, the former mayor Boris Johnson, who had locked horns with the unions on ticket office closures and Night Tube plans, said he hoped services would get underway by July.
The new London Mayor Sadiq Khan plans to travel on the first Night Tube train on the Victoria line from Brixton later.
He said: “I’m really excited. Lots of people need to get to work late in the night or home from work – doctors, nurses, porters, security guards – but also it will be a massive boost to the night time economy.
“Think of the theatres, the live music venues, the restaurants. I’m really pleased and proud that finally the Night Tube is here.
“Boris Johnson deserves credit for talking about the Night Tube, but it was important to get the details right. I’m really pleased and proud that finally it’s going to happen.”
The night service will be rolled out on the Jubilee, Piccadilly and Northern lines in the autumn.
There are also plans to expand the service to parts of the Metropolitan, Circle, District, and Hammersmith & City lines after modernisation and on parts of the London Overground in 2017 and the Docklands Light Railway by 2021.
Passengers will pay off-peak fares and day travelcards will be valid but will expire at 04:30.
About 100 police officers will be on patrol to allay any safety fears and eight new bus routes will now run 24-hour services to go hand-in-hand with the night services on the Tube.
The new 24-hour bus services will run on Friday and Saturday nights to complement the Night Tube and ensure customers travelling in the early hours of the morning have easy options to get home.
Night Tube services begin on the Central and Victoria lines on Friday and Saturday nights from 19 August, and at the same time the following bus routes will have 24-hour services for the first time:
34 (Barnet Church to Walthamstow Central)
123 (Ilford High Road to Wood Green)
145 (Leytonstone to Dagenham)
158 (Stratford to Chingford Mount)
296 (Ilford Broadway to Romford)
E1 (Greenford Broadway to Ealing Broadway)
W3 (Finsbury Park to Northumberland Park)
W7 (Finsbury Park to Muswell Hill Broadway).
The Mayor of London, Sadiq Khan, said: ‘The Night Tube is going to transform our city as for the first time tube passengers will be able to travel swiftly across the Capital throughout the night.
‘The safety and security of Londoners is vital, and it’s why we’ve invested in new police officers on the Tube and it’s why we’re bringing in these brand new 24-hour bus services.
‘The routes will go hand-in-hand with the Night Tube to help Londoners get to and from their front door throughout the night.
‘It’s another key step in helping everyone travel quickly and safely at night, and another boost to unlocking the full potential of our night time economy.’
The new services will run every 30 minutes throughout Friday and Saturday nights, other than the W7, which will run every 20 minutes. The enhancements follow the introduction of seven new night bus services already made in anticipation of the introduction of the Night Tube.
Mike Weston, TfL’s Director of Buses, said: ‘These additional 24-hour bus services will enhance our London-wide, night time bus network and complement the Night Tube, making it easier for our customers to get home in the early hours of the morning.
‘This will enable customers to make the most of London at night and will in turn help to boost the Capital’s vibrant and growing night-time economy.’
There are a total of 123 bus routes that operate overnight, of which 73 are 24-hour services and 50 are night bus routes.
The number of night bus services has increased significantly in recent years with passenger numbers more than doubling since 2000. More than half the users are people travelling to or from work.
Ridership levels on all night bus services will be monitored to see how demand changes following the introduction of the Night Tube.
London has one of the most extensive and accessible bus networks anywhere in the world. TfL’s bus network comprises around 700 routes across Greater London, operated by 7,900 buses at peak times, carrying almost 2.4 billion passengers every year, which equates to half of all bus journeys made in England.
Since TfL was formed in 2000 it has invested strongly in London’s bus network – resulting in a 69% increase in passenger numbers.