Two major media companies are to combine in an all-stock merger.

CBS and Viacom have entered into a definitive agreement that would create a combined company with more than US$28bn (€25bn) in revenue.

The combined entity, to be called ViacomCBS Inc., will offer multi-platform, premium content in markets across Europe, the US, Latin America and Asia.

This includes the largest television business in the US, with the highest share of broadcast and cable viewing across all key audience demographics.

It will also include the film studio, Paramount Pictures, which has been a producer and global distributor of filmed entertainment for more than a century.

Its franchises include 'Star Trek' and 'Mission: Impossible'.

The joined portfolio includes brands like Comedy Central, MTV and Nickelodeon.

Viacom headquarters in Times Square, New York in December 2016 | Image: Richard B. Levine/SIPA USA/PA Images

It will also have one of the largest libraries of intellectual property - made up of over 140,000 TV episodes and 3,600 film titles.

The combined company will have more than 750 series currently ordered to or in production.

The firm says it will reach more than 4.3 billion cumulative TV subscribers.

It will operate broadcast networks in the UK, Argentina and Australia - as well as pay-TV networks across more than 180 countries.

Bob Bakish, president and CEO of Viacom, will become president and chief executive of the combined company.

On the merger, he said: "Today marks an important day for CBS and Viacom, as we unite our complementary assets and capabilities and become one of only a few companies with the breadth and depth of content and reach to shape the future of our industry.

"Our unique ability to produce premium and popular content for global audiences at scale - for our own platforms and for our partners around the world - will enable us to maximize our business for today, while positioning us to lead for years to come."

Joe Ianniello, president and acting CEO of CBS, will become chairman and CEO of CBS.

He will oversee all CBS-branded assets in his new role.

The CBS Television City Studio in Los Angeles, California | Image: Ronen Tivony/SIPA USA/PA Images

This is the latest in a line of big mergers in recent years.

Back in 2016, AT&T agreed to buy media group Time Warner for €78.4bn.

Time Warner's portfolio of assets include the Warner Bros motion picture studio, news network CNN and HBO - which produced TV shows such as 'Game of Thrones' and 'Sex and the City'.

Its film franchises include 'Harry Potter', DC Entertainment, and Lego - and its TV series productions feature 'The Big Bang Theory' and 'Gotham'.

While in 2018, US cable giant Comcast outbid 21st Century Fox in an auction to buy the UK company Sky.

Both US entertainment firms had been engaged in a lengthy bidding war for Sky.

The successful offer valued the company at more than €33.4bn.