Twelve trains an hour are scheduled to run on the line
Tube workers have held a protest over the East London Line on the day the full service began for commuters.
Members of the RMT union held the demonstration outside Whitechapel Underground Station, in east London.
The union said that the private firm London Overground (LOROL) prioritised shareholders over passengers.
But Transport for London (TfL) said a funding condition for the upgrade was for the line to be run by a different firm to TfL.
The route, which is a part of London Overground network, is the first phase of a £1bn extension of the line.
RMT General Secretary Bob Crow said: "£1bn has been spent on this upgrade and every single penny of taxpayer subsidy and fare revenue should be invested to improve services and not be removed from the industry in shareholder dividends."
A Transport for London spokesman said: "It was a Department for Transport condition on the funding of the upgrade that the operation of the London Overground railway be run by a train operating company under a concession agreement."
"The upgrade, conversion and extension of the former East London Line created a one-off opportunity to improve transport links in some of the most socially deprived areas of London," he added.
Twelve trains an hour are scheduled to run from Dalston Junction, north London, to West Croydon, New Cross and Crystal Palace in south and south-east London.
Evening and weekend services began on the East London Line last weekend.