As the official candidate he ran successfully for election as deputy for the 5th college of Gers (Mirande) on 27 December 1834.

He sat in the center, supported the government, and became noticed as a skilled speaker on a variety of topics.

[4] Lacave-Laplagne returned to his seat in the Chamber with the conservative majority, and continued to participate in all discussions about public works and finance.

[2] Lacave-Laplagne was again given the Finance portfolio when Georges Humann died on 25 April 1842, and retained it until 8 May 1847.

He was involved in questions that included reducing the size of the army, police, patents, recruitment, conversion of pensions, postal reform, taxes on newspapers and periodicals, railway concessions, customs and salt taxes.

When Louis-Antoine Garnier-Pagès, Finance Minister in the Provisional Government (24 February 1848 to 9 May 1848), criticized the financial administration of the July Monarchy, Lacave-Laplagne issued a rebuttal.