He was born on 6 December 1894 in Antanašė near Kaunas. In 1917, he completed studies in law and political science in Lausanne and Fribourg. He was a close associate of Henryk Sienkiewicz, the then President of the Swiss General Committee to Aid War Victims in Poland based in Vevey, Switzerland. In 1919, he became personal secretary to Roman Dmowski and attended the Paris Peace Conference.

Since 1921, he worked at the Ministry of Foreign Affairs and was a diplomat in Paris, Rome and Portugal. In 1937, he took up a diplomatic post in Japan. After the outbreak of war, when information about the forced resettlement of thousands of Polish citizens deep into the USSR and the fate of the deportees began to arrive at the Polish embassy in Tokyo, Romer established Social Welfare Departments at the Polish post, which by the end of May 1941 had sent 745 people in the USSR money and parcels containing food, clothing and medicines. The second large group of Polish citizens whom the embassy rushed to help were refugees from countries occupied by the Soviets, who reached Japan thanks to visas issued by the Japanese consul in Kaunas, Chiune Sugihara. 

In October 1940, Romer founded the Polish Committee to Aid War Victims in Tokyo, chaired by Zofia Romer, the ambassador's wife. Romer himself organised a passport and visa campaign. Among other things, he provided Jewish refugees from Poland and Lithuania with 250 asylum visas to Canada. After the Polish diplomatic post in Tokyo was closed down, Tadeusz and Zofia Romer continued to help refugees in Shanghai. The names of thousands of people who were rescued are contained in the Shanghai Ledger (currently located in the Library of Congress in Washington DC), which was written at that time. The Romers were awarded the Righteous Among the Nations medal for their work.

On 15 September 1942, he served as a Polish ambassador to the USSR in Kuybyshev. He was an advocate for the rights of Polish citizens deported to Siberia, the Arctic and Central Asia, as well as opposed to the Soviets' decision to deprive them of Polish citizenship. He helped Polish citizens who had been forcibly deported to the USSR; according to the embassy, in 1942-1943, the number of Polish citizens in the USSR receiving humanitarian aid amounted to 265,501. On the night of 25-26 April 1943, he did not accept a letter from the USSR Minister of Foreign Affairs, Vyacheslav Molotov, unilaterally breaking diplomatic relations between the USSR and Poland. 

After leaving the Soviet Union, he became representative of the government of the Republic of Poland in the Middle East, and then, from 14 July 1943 to 24 November 1944, served as the Minister of Foreign Affairs in Stanisław Mikołajczyk's government.

He remained in exile, first in London and then in Canada, where he died on 23 March 1978.