Duncan MacLaren made this statement Friday in a press release to announce the organization's 18th general assembly, to be held June 3-9.
Meanwhile, the leaders of major industrial countries will meet at the G-8 summit in Heiligendamm, June 6-8.
The secretary-general said: "The Caritas General Assembly and the G-8 will be more than a tale of two summits, they will be a tale of two worlds.
"On one hand, you have the leaders representing the interests of the world's rich countries with a combined gross domestic product of over $30 trillion.
"On the other hand, you have representatives of civil society working for the world's 3 billion people living on less than $1 a day."
MacLaren said that "G-8 leaders must live up to their promises on aid." He added that "there is backsliding with the commitments made" two years ago at the summit held in Gleneagles, Scotland.
"Caritas wants G-8 countries to deliver on promises to increase aid to 0.7% of national income, and to ensure that aid is used effectively to end poverty. Millions of the poor will suffer as a consequence of these broken promises," he added.
Keynote speakers for the Caritas meeting will include Nobel Peace Prize laureate Wangari Maathai and president of the Pontifical Council for Justice and Peace, Cardinal Renato Martino.