Deconchy fought in several actions during the War of the Third Coalition. Transferred to Spain, he was acting commander of a light infantry regiment in the VI Corps for a time before being elevated to colonel in September 1810. He participated in the 1810 French invasion of Portugal and led his regiment at Redinha during the retreat. He was promoted general officer in February 1813 and fought against the Spanish guerillas. In August 1813 he transferred to Italy where he led a brigade in the army of Eugène de Beauharnais until the end of the fighting in 1814. He stayed in favor with the Bourbons and was elevated to the rank of lieutenant general in 1821. He led a division in the 1823 French intervention in Spain and died during the blockade of Pamplona.