Starting March 15, Messenger users will no longer be able to sign in on desktop clients and will have to upgrade to Skype. Between now and then Messenger users will be able to sign into Skype using a Microsoft account.
This move ties into Microsoft's decision to retire the Windows Live brand with the launch of Windows 8.
Advertisers on Messenger are "being encouraged to explore" advertising opportunities on Skype, where they will potentially reach 47.3 million users, compared with Messenger's user base of 5.3 million.
Depending on user overlap between the two platforms, the Skype user base should increase to a degree following the migration.
Microsoft acquired Skype in October 2011 for US$8.5 billion.
Ad formats available on Skype include conversation ads, homepage takeover ads and mobile ads.
"The consumer experience was top of mind when we made the decision to retire Windows Live Messenger and encourage customers to move to Skype," said a Microsoft spokesperson. "From an advertising perspective, the move gives Skype an even broader global reach and marketers access to premium branded experiences on Skype."