Publicis Media is dropping Blue 449 as a brand in the UK and the US and merging it with Spark Foundry in the latest sign of large agency groups wanting to streamline their operations.
About 200 Blue 449 staff in the UK and around 250 in the US will join Spark Foundry.
Blue 449 will continue to operate in only one market – France.
The agency’s future has looked in doubt since March, after parent company Publicis Media paid £25m to buy out minority shareholder M&C Saatchi.
Blue 449 was dropped as a brand at the time, except in three markets, the UK, France and the US, and it became part of Spark Foundry’s global network.
Sue Frogley, chief executive of Publicis Media UK, said it now made sense to drop Blue 449 in the UK from the start of January 2020.
"Publicis Media is a brand-led organisation and integrating Blue 449 and Spark Foundry will create a powerful brand that is well-positioned to drive strong results for clients," she said.
The enlarged Spark Foundry will have about 300 UK staff and add Blue 449 clients such as Asda and Dixons Carphone.
Blue 449 was already a top 10 UK media agency, based on a 2018 estimate of Nielsen billings, and Spark Foundry will likely have close to £300m in billings now.
Lindsay Turner, chief executive of Spark Foundry UK, said: "This feels like the perfect time to bring Blue 449 under the Spark Foundry brand in the UK.
"The two agencies have been naturally coming together both in its leadership team and in the cross-pollination of agency strengths, so this feels a very natural next step."
Blue 449, which was previously known as Walker Media, was founded as an independent agency in London in 1998.
Turner knows Blue 449 well because she has worked at the agency since 2011 and is a former managing director.
She has held dual roles as chief executive of Blue 449 and Spark Foundry in the UK since April.
Turner replaced Simon Davis, long-serving UK chief executive of Blue 449, who quit as he disagreed with the strategy of bringing the agency together with Spark Foundry.
Chris Boothe, global brand president of Spark Foundry, heads the network and oversees the US operation.
Pascal Crifo remains chief executive of Blue 449 in France to serve domestic clients.
Publicis Media still has five global agency brands – Digitas, Performics, Spark Foundry, Starcom and Zenith – despite dropping Blue 449.
Other big groups have also been reducing agency brands to simplify their operations.
Dentsu Aegis Network merged Fetch, 360i and ICUC to form Dentsu X in June in the UK and moved its media investment capabilities from trading arm Amplifi into Carat and Vizeum in November.
WPP’s Group M also dropped mPlatform as a brand for its data and technology division last month as part of a reorganisation to improve "consistency".