Mociulschi started his military career in 1910 at the Infantry Officers' School, from which he graduated in 1912, with the rank of Second Lieutenant. He took part in the Second Balkan War, and in 1916, at the beginning of the Romanian campaign of the First World War, he commanded the 10th Company of the 29th Infantry Regiment, holding the Lieutenant rank. For his valor during the Oituz and Soveja battles he was decorated by King Ferdinand and General Berthelot, the commander of the French Military Mission in Romania, and promoted to the rank of Captain. After the end of the war Mociulschi was promoted to Major, and in 1932 he was given the command of a mountain battalion in Sighetu Marmației, with the rank of Lieutenant-Colonel. In 1937 Mociulschi was promoted to Colonel. During World War II he fought on the Eastern Front against the Soviet Union and was promoted to Brigadier General in 1942 and to Major General in 1944.
Leonard Mociulschi was the commander of the Romanian troops that entered on 24 September 1944 the village of Ginta. The majority of the villagers in Ginta were Hungarians, with some Romanian families living there as well. Located in Southern Transylvania after the Second Vienna Award, Ginta had been occupied shortly by Hungarian forces when, on 23 September 1944 a Romanian soldier was shot out of a window in the village. According to another source, fierce street fighting took place in the village on 24 September. Under the pretext that the village was resisting the Romanian Army, Mociulschi ordered as retaliation the burning of the village. The Romanian Captain Teodor Brîndea, another officer and a soldier with a machine gun gathered the people from the streets, their yards and houses, took them to the edge of the village and executed them. Two days after the massacre the Romanian Army did not give the dead a proper burial and instead dumped the bodies of the villagers in a mass grave. Thus Mociulschi was responsible for the death of at least 47 unarmed civilians in the village, from the age of 2 to the age of 71, although different sources mentioned that the massacre was perpetrated by the Tudor Vladimirescu Division. Mociulschi was never charged for the massacre. Zoltán Boros, the son of the local Reformed priest and a survivor of the massacre, was then 5 years old. On that day his father was in a labor camp. He recalled that a local Romanian doctor, Augustin Pop, hid him and his then-seven-year-old sister in a dark room, and they were asked by their mother not to make any noise. Later on his mother told him that the doctor dressed her as a maid so that it would not raise any suspicion when the Romanian officers arrived. One of the officers asked, "Well, we know the priest is in the camp, but where's his wife?" The doctor answered that she had already left with the retreating Hungarians. During the Ginta massacre a villager named Lájos Togyinka showed what "Until death do as apart" means because Togyinka was Romanian and the Romanian soldiers did not want to execute him, however his wife was Hungarian and Togyinka instead of fleeing chose death by the side of his wife. The officer in charge with the execution, Bridea, also ordered the 13 and 17 year old sons of Togyinka to be also executed. The grave of the murdered Togyinka family reads: "Kioltott ártatlan vérök annak a tanúja, hogy ártatlanul haltak. Aludjatok drága szereteink békén az Úrjézusban. A boldog viszontlátásra" The Ginta massacre was even marked as taboo by the Romanian government until the early 2000s.
