The platform will enable users to view programs up to seven days after their original broadcast free of charge, the companies said on Friday.
The move follows similar actions in other countries by free-to-air broadcasters chasing mainly younger audiences who spend more time online than in front of a television set.
In Britain, the state-owned BBC has clubbed together with commercial broadcasters ITV, Channel 4 and RTL's soon-to-be-sold UK arm Five as well as telecoms providers BT and TalkTalk to develop an Internet TV project named Canvas.
And in the United States, TV networks NBC, ABC and Fox own the well-established Web video service Hulu, which has recently added a paid-for subscription service to its advertising-funded offerings, and is making its services available on devices including Apple's iPad.
Hulu generated an estimated $100 million in advertising revenue last year.
ProSiebenSat1 and RTL Deutschland, the German unit of pan-European broadcaster RTL Group, already offer free and paid content on their individual platforms Maxdome and RTL now respectively in Germany, Europe's biggest TV market.
Like other broadcasters they are keen expand in the Internet TV market betting that online advertising will compensate slumping ad revenues and fragmenting audiences.
The planned platform is subject to approval by the European Commission Directorate General and an application for approval was submitted on Friday.
(Reporting by Nicola Leske in Frankfurt, additional reporting by Georgina Prodhan in Helsinki; Editing by Sharon Lindores)