Among the services to benefit will be commuter trains between Hastings and Charing Cross and Canon Street, and Dartford and Gravesend to Victoria.
There will also be extra peak time services from Maidstone East and Ashford to London.
The three new trains are Class 377s, bringing the total number in the operator’s fleet to 36.
Scott Brightwell from South Eastern Railway, said: “This latest timetable change meets rising demand by increasing services where needed and adding space for extra comfort at the busiest times.
“Customers can check their amended services now as journey planners have been updated online and full details of the changes can be found on our website.”
