He enrolled in high school, however, due to financial problems he was forced to abandon it and work as an apprentice in an upholstery workshops.

At the end 1902 he departed for Paris, France, however he kept contacts with Romanian workers' movement, occasionally sending articles for the socialist newspaper 1 Mai ("May Day").

Alecu Constantinescu himself began in 1906 a tour of Romanian cities, helping organise the local workers, in the hope of creating an unified national trade union.

Due to his activism among the local workers in support of the peasants he was imprisoned for lèse majesté, however the Fălticeni court cleared him of charges few weeks later.

[3] In late June he participated in the second Conference of trade unions and socialist circles that took place in Galaţi, and in August he was part of the Romanian delegation to the Stuttgart Congress of the Second International, along Christian Rakovsky, N. D. Cocea and Andrei Ionescu.

[3] Between 1906 and 1910 he organised Cercul Amicilor ("The circle of friends"), an association that offered political education and guidance for the trade union leaders from Bucharest and the other Romanian cities.

In August 1916, after Romania joined the war on the side of the Entente, he was the founder and leader of a Central Committee for anti-war and anti-imperialist action.

[1] He succeeded in creating a clandestine "maximalist faction", favourable to the Bolsheviks, and continued to spread anti-war propaganda.

[5] As a 20,000 lei reward was put on his head, he was forced to leave for Bulgaria in early 1921, eventually making his way to Soviet Russia.

Set free after Romania changed sides and joined the Allies in August 1944, he worked for the Bucharest section of the Romanian Communist Party.