The group was established following the passing of Security Council Resolution 128 on 11 June 1958 in response to the 1958 Lebanon crisis, which had been triggered by an armed rebellion against the Camille Chamoun's government in May.

The advanced party began reconnaissance the following day,[1] and the first official meeting of the group's governing committee taking place in Beirut on 19 June.

Over the following months, the observers were able to determine that only a small amount of arms had been brought through the border areas and that the movement of personnel for military purposes was largely non-existent.

[9] Military personnel were drawn from 21 countries: Afghanistan, Argentina, Burma, Canada, Ceylon, Chile, Denmark, Ecuador, Finland, India, Indonesia, Ireland, Italy, Nepal, Netherlands, New Zealand, Norway, Peru, Portugal, Sweden and Thailand.

Events in Jordan, and the political backdrop of the Cold War, also impacted the ongoing viability of the mission and gave impetus for the withdrawal of foreign troops from Lebanon.

[11] In early November, diplomatic relations between Lebanon and the United Arab Republic improved and the Lebanese government officially asked the UN to withdraw its earlier concerns.