The posts, which will be advertised from February, were announced as London Underground unveiled a £1m revamp of its Acton training centre, including new equipment and learning facilities.
Apprentices at the centre are studying a range of essential topics, including signalling, track engineering and project planning.
The 100 new posts follow the recruitment of 86 apprentices who joined TfL in September.
The positions will contribute towards the Mayor’s pledge to create 250,000 apprenticeships by 2016, a target the London Assembly recently warned he was in danger of missing.
Mike Brown MVO, Managing Director of London Underground and London Rail, said: “All our apprentices are helping us to support over 30 million journeys every day as we continue to invest billions of pounds in our transport network to meet the needs of London’s growing population to support jobs, homes and economic growth.
“It is clearly essential that we have the right people with the right skills to enable us to deliver for the city and its people.”
