The son of a prosperous Protestant family of Dutch descent, Hymans was educated in law and history at the University of Brussels, where he joined the faculty in 1897.
He was elected to Parliament in 1894. As a Liberal during an era dominated politically by Belgium s Catholic party, he had no prospects for a cabinet seat, but he promoted such successful initiatives as the end to the king's personal control over the Congo (1908) and the reform of Belgium's system of conscription (1909).
World War I opened the door to national office. Hymans led a successful diplomatic mission to the United States in August/September 1914. There he made a direct appeal to President Woodrow Wilson for food and moral support. In February 1915 he took the post of ambassador to Great Britain. When the Belgian government in exile refused to link itself formally to the Entente, Hymans' concern over Belgium's diplomatic isolation led him to work toward an alternative.
His efforts produced the Declaration of Sainte-Addresse (February 1916): in this, Britain, France, and Russia pledged to include Belgium in the peace negotiations. The Belgians also received a promise that the future settlement would include a restoration of Belgium's independence, as well as monetary compensation from Germany for the ravaged nation. In October 1917 Hymans joined the government in exile in Le Havre as minister of economic affairs. In January 1918, he became Belgium's new foreign minister. By the closing months of the war, Hymans had become the spokesman for basic changes in Belgian foreign policy.
It was Hymans who led Belgium s delegation to the Peace Conference at Versailles. He was, first of all, determined to end Belgium's neutral status; imposed in 1839 and guaranteed by the great powers, it had been a useless paper shield in 1914. He also sought to place Belgium first in line to receive reparations payments from Germany. In these areas Hymans emerged victorious. Other ambitions went unfulfilled. Belgium did not obtain substantial territorial additions, only the small enclaves of Eupen and Malmédy along with a number of protectorates in Africa. Hymans had hoped to annex substantial portions of Holland and all of Luxembourg. Skilled Dutch diplomacy blocked the former goal; France's own ambitions toward Luxembourg killed the latter. As the Luxembourg issue illustrated, Hymans found his country's wartime associates willing to pursue their ambitions with minimal regard for Belgian expectations. He was even more disappointed to find the great powers in the Council of Five shaping the peace settlement to the exclusion of the smaller nations.
Hymans emerged as a spokesman for the minor powers at Versailles. This in turn led to his selection as president of the first assembly of the League of Nations. He went on to direct the Belgian Foreign Ministry almost without a break from 1924 to 1935, a period marked by the successful negotiation of the Locarno Treaties. In 1940, however, Hymans fled the second German invasion of his country in his own lifetime. He did not survive to see the liberation but died in Nice, March 6,1941.
Paul Hymans helped form the customs union of Belgium and Luxembourg (Belgium-Luxembourg Economic Union) in 1921 and played a leading part in negotiating the Dawes Plan in 1924. In 1928, he signed the Kellogg-Briand Pact for Belgium.
He was a freemason, and a member of the lodge Les Amis Philanthropes of the Grand Orient of Belgium in Brussels. Paul Hymans is interred in the Ixelles Cemetery in Brussels.