In 1971, IMU President Henri Cartan announced the new IMU Bulletin in his preface to IMU Bulletin No. 1 (1971), page 3:

"The International Mathematical Union, in its present form, has completed twenty years of existence. Reports of the Union's activities during this period have been sent out to member-countries as required under the statutes and by-laws. Some of them have also been published, by arrangement, in the Bulletin of the Austrian Mathematical Society. In view of the expanding role of the Union, it has seemed desirable to keep a continuous and easily accessible record of its activity. This is now being done in the form of an IMU Bulletin, of which this is the first issue."

Since then, the IMU Bulletin has been published as an independent journal and distributed to IMU members. After a period of hybrid publication in both print and digital formats, the IMU Bulletin has only been available electronically since volume 69, December 2017.  All issues of the IMU Bulletin are freely available through the IMU Archive.

Between 1952 and 1970, a predecessor of the IMU Bulletin appeared as "International Mathematical News" in the "Nachrichten der Österreichischen Mathematischen Gesellschaft (ÖMG)". Indeed, when the IMU was re-established in 1951, a way was needed to publish news, reports and any other information and to distribute it to the members. As Olli Lehto writes in his book Mathematics without Borders (1998), pages 96-97:

"The Rome Assembly [1952] agreed that the Executive Committee should negotiate with the Österreichische Mathematische Gesellschaft (Austrian Mathematical Society) a contract for the publication of an international mathematical news bulletin continuing in a way suitable to the needs of the Union the work already undertaken by the ÖMG. The contract was concluded, and IMU news appeared for many years in the Austrian Internationale Mathematische Nachrichten [...]"