More than 300 members will walk out for 48 hours from 00.01am on Monday 19 February 2024 until 11.59pm on Tuesday 20 February 2024, and again from 00.01am on Monday 4 March 2024 until 11.59pm on Tuesday 5 March 2024.
Among those taking action are security, station, revenue and control staff.
The announcement comes on the first day of a separate series of rolling strikes being organised by train drivers union, Aslef, which has shut down some of the busiest rail routes in the country.
The RMT said that Arriva Rail London, which runs the London Overground on behalf of Transport for London (TfL), has offered a below inflation pay offer, and that their members over overwhelmingly voted for a walkout.
Mick Lynch, general secretary of the RMT, said: “London Overground workers do an important job delivering services for Transport for London and supporting passengers on journeys throughout London.
“Our members are furious that they have been given a below inflation pay offer and want to see an improvement that represents the value they bring to the company.
“If this dispute cannot be resolved then RMT is more than prepared for a sustained period of industrial action to get London Overground workers the pay rise they deserve.”
The boss of Arriva Rail London, Steve Best, told The Independent that the RMT was yet to notify the company about dates for industrial action.
“We are hugely disappointed to hear of the RMT union’s decision to stage industrial action on the London Overground in February and March. We believe we have offered a good pay award in comparison not only to our industry, but other industries and businesses in the UK too. We remain committed to engaging with the RMT in the hope of resolving this dispute,” he said.
“We remain in a cost-pressurised environment, and it is therefore important for us to offer our colleagues a pay award that is affordable and sustainable. We are committed to delivering fair pay awards for our employees, as well as protecting long-term job security for our people. We are putting robust contingency plans in place should any industrial action go ahead, to ensure the safety and security of our people and customers."
A TfL spokesperson said: "We encourage the RMT to continue engaging with Arriva Rail London to try to resolve this dispute and avoid impacting our customers with strike action.”
From 30 January, train drivers belonging to Aslef are stopping work region-by-region over the course of a week between Tuesday 30 January and Monday 5 February. Thousands of trains will be cancelled on each day.
The effect is exacerbated by a nine-day ban on overtime running from 29 January to 6 February.