[1][5] In 1948, Weaver was sent as a union representative to the National Defense Conference on Negro Affairs, a meeting at The Pentagon organized by U.S. Secretary of Defense James Forrestal, whose goal was "introducing to the services in a systematic and documented way the complaints of responsible black leaders while instructing those leaders in the manpower problems confronting the postwar armed forces."

[6] Soon thereafter, President Truman's Executive Order 9981 (July 26, 1948) abolished discrimination "on the basis of race, color, religion or national origin" in the United States Armed Forces, and led to the re-integration of the services during the Korean War (1950–1953).

[7] Beginning in 1950, Weaver worked on international labor issues as a special assistant to W. Stuart Symington, who chaired the National Security Resources Board and later the Reconstruction Finance Corporation.

[2][8] Symington credited Weaver with substantial help in stopping speculation that drove up tin prices, calling him in 1969 "one of the ablest public servants we have today.

"[9] During the 1950s, Weaver spent time abroad as a representative of the International Confederation of Free Trade Unions (ICFTU), with the goal of assisting foreign labor leaders.

[1][10] In 1955, ICFTU official Jay Krane described Weaver as "one of the outstanding Negro trade unionists in the United States and ... a leading figure in the fight against discrimination and segregation.