From 1926 to 1934, he served as Polish envoy in several European countries in Riga, Latvia, from 1926 to 1929; in Vienna, Austria, from 1931 to 1932; and in Moscow, Soviet Union from 1933 to 1934.

Upon the Invasion of Poland in September 1939, Łukasiewicz energetically lobbied the French government and military officials to fulfill their obligations towards the Franco-Polish Alliance and the Kasprzycki-Gamelin Convention.

After the defeat of France in 1940, Łukasiewicz wrote a manifest to President Władysław Raczkiewicz criticising Sikorski's decision to send a manifest to Stefan Litauer that proposed the creation of a 300,000-strong Polish Army under the command of the Soviet Union.

Łukasiewicz additionally criticized Sikorski for squandering Polish forces in France to the enemy during the hasty retreat in May 1940, the loss of Polish bullion and for simultaneously assuming the seat of Prime Minister and General Inspector of the Armed Forces.

Łukasiewicz's manifest greatly influenced Raczkiewicz's decision to dismiss Sikorski's premiership on July 19, 1940.