Born in Bacău, he was the son of paharnic (royal cup-bearer) Gheorghe Lecca (reportedly a descendant of Leca of Cătun), who died the year after the son was born; and of Maria Negură. Together with his brothers Ioan and Dimitrie, he attended the Cavalry School at Saumur. After returning home in 1854, he took part in the Crimean War. After leaving army service, he served as prefect of Bacău County in 1866, and then as deputy and senator. In early 1882, he was named Finance Minister in the Liberal government of Ion C. Brătianu, serving until his death (in Bacău).
He had four children with his first wife Mariana Mălinescu (d. 1875), and a son with his second, Clara Negură (his first cousin, 1852–1909). Two of his sons, Caton (1860–1913) and Jean (1863–1898), entered politics.
- Rădulescu, Mihai Sorin. "Familia Lecca din Moldova și avatarurile ei peste timp". Historia (in Romanian). Retrieved December 26, 2020.
- "Descoperire senzațională în Arhivele Naționale: Caietele cu însemnări ale politicianului băcăuan Iuniu Lecca". www.desteptarea.ro (in Romanian). January 27, 2017. Retrieved December 26, 2020.
- Octav George Lecca, Familiile boerești române, p. 318. Bucharest: Editura Minerva, 1899