Having completed the obligations that had called him to Lisbon, Mouzinho da Silveira opted not to return to Castelo de Vide, where he might have joined the magisterium (the legal body of Portuguese magistrates).

Instead, he took office on 1 March 1809, as a juiz de fora (itinerant judge) for Marvão, where he had lived over the previous three years (preparing the defenses during the Napoleonic invasion).

In February 1821, he was entrusted with the collections for the Ministry of Finance in Estremoz, in addition to visiting the comarcas of Évora and Ourique, which he was unable to complete, being dispatched on 11 April to the Alfândega Grande do Açúcar (Great Sugar Customshouse) in Lisbon, where he began exercising his role on 15 May.

Referring to this nomination, Mouzinho wrote: "Being administrator of the customs house, I was obligated, against my will, to be Minister of Finance on 29 May 1823, and surviving the reestablishment of the absolute monarchy, I was fired on the 15th and returned to my job in the customshouse, retaining my honors as Minister"[1] In this short passage through the corridors of government, Mouzinho was able to promulgate the decree of 12 June 1823, revoking the taxes and 10% special fees, which were established by law in March 1823.

On 6 June, he was also asked to join the Chamber of Deputies' Finance Commission, the council responsible for collecting funds and loans necessary to subsidize the Liberal cause.

While in Paris, he was invited to accompany Peter IV during his campaign to return Portugal to a liberal monarchy, and departed on 25 January 1832 for Terceira, from Belle-Isle.

On 9 August, in complete disagreement with the progress of public finances, particularly with loans obtained by Palmela, and harassed by his opponents, who accused him of radicalism and folly, he sought a resignation from the positions he held, which was granted on 3 December 1832 by Pedro IV.

He returned to Portugal on 11 September 1834, and joined the Chamber of Deputies, where he remained until 1836, always uncompromising in his defense of his legislation and maintaining a constant intervention in matters of the public finances.

José Xavier Mouzinho da Silveira died in Lisbon, on 4 April 1849, after a fall on his staircase, caused when he was moving a piano, resulting in his being crushed.

Starting in 1875, with erection of a monument in the parish of Margem, municipality of Gavião, sculpted by Célestin Anatole Calmels, many Portuguese community have honored this notable citizen.

While, in the secondary centenary of his birth (1980) a commemorative monument was inaugurated in Castelo de Vide, many of the cities of the country have homages to the Mouzinho da Silveira, including schools and roadways.