The Panthéon was twice restored to church usage in the course of the 19th century—although Soufflot's remains were transferred inside it in 1829—until the French Third Republic finally decreed the building's exclusive use as a mausoleum in 1881.

The successive changes in the Panthéon's purpose resulted in modifications of the pedimental sculptures and the capping of the dome by a cross or a flag; some of the originally existing windows were blocked up with masonry in order to give the interior a darker and more funereal atmosphere,[2] which compromised somewhat Soufflot's initial attempt at combining the lightness and brightness of the Gothic cathedral with classical principles.

In 1851, Léon Foucault conducted a demonstration of diurnal motion at the Panthéon by suspending a pendulum from the ceiling, a copy of which is still visible today.

[5] King Louis XV vowed in 1744 that if he recovered from his illness he would replace the dilapidated church of the Abbey of St Genevieve with a grander building worthy of the patron saint of Paris.

In 1755 The Director of the King's public works, Abel-François Poisson, marquis de Marigny, chose Jacques-Germain Soufflot to design the church.

The outermost dome, visible from the outside, is built of stone bound together with iron cramps and covered with lead sheathing, rather than of carpentry construction, as was the common French practice of the period.

On April 4, 1791, the Assembly decreed "that this religious church become a temple of the nation, that the tomb of a great man become the altar of liberty."

[11] The ashes of Voltaire were placed in the Panthéon in a lavish ceremony on 11 July 1791, followed by the remains of several revolutionaries, including Jean-Paul Marat, replacing Mirabeau and of the philosopher Jean-Jacques Rousseau.

In the rapid shifts of power of the Revolutionary period, two of the first men honored in Pantheon, Mirabeau and Marat, were declared enemies of the Revolution, and their remains were removed.

[12] Napoleon Bonaparte, when he became First Consul in 1801, signed a Concordat with the Pope, agreeing to restore former church properties, including the Panthéon.

It combined the secular and religious aspects of the church; it showed The Apotheosis of Saint Genevieve, conducted to heaven by angels, in the presence of great leaders of France, from Clovis I and Charlemagne to Napoleon and the Empress Josephine.

The sculpture on the pediment by Jean Guillaume Moitte, called The Fatherland crowning the heroic and civic virtues was replaced by a religious-themed work by David d'Angers.

In 1822 François Gérard was commissioned to decorate the pendentives of the dome with new works representing Justice, Death, the Nation, and Fame.

Beginning in 1874, the interior was redecorated with new murals and sculptural groups linking French history and the history of the church, by notable artists including Puvis de Chavannes and Alexandre Cabanel, and the artist Antoine-Auguste-Ernest Hébert, who made a mosaic under the vault of the apsidal chapel called Christ Showing the Angel of France the Destiny of Her People.

The Third Republic governments also decreed that the building should be decorated with sculpture representing "the golden ages and great men of France."

The principal works remaining from this period include the sculptural group called The National Assembly, commemorating the French Revolution; a statue of Mirabeau, the first man interred in the Pantheon, by Jean-Antoine Ingabert; (1889–1920); and two patriotic murals in the apse Victory Leading the Armies of the Republic to Towards Glory by Édouard Detaille, and Glory Entering the Temple, Followed by Poets, Philosophers, Scientists and Warriors, by Marie-Désiré-Hector d'Espouy (1906).

[15] The short-lived Fourth Republic (1948–1958) following World War II pantheonized two physicists, Paul Langevin and Jean Perrin; a leader of the abolitionist movement, Victor Schœlcher; early leader of Free France and colonial administrator Félix Éboué; and Louis Braille, inventor of the Braille writing system, in 1952.

Under the Fifth Republic of President Charles de Gaulle, the first person to be buried in the Panthéon was the Resistance leader Jean Moulin.

Modern figures buried in recent years include Nobel Peace Prize winner René Cassin (1987) known for drafting the Universal Declaration of Human Rights; Jean Monnet (1988) who was a moving force in the creation of the ECSC, the forerunner of the EU, was interred in the 100th anniversary of his birth; Nobel laureates physicists and chemists Marie Curie and Pierre Curie (1995); the writer and culture minister André Malraux (1996); and the lawyer, politician Simone Veil (2018).

Looking up from the crossing of the transept beneath the dome, the painting by Jean-Antoine Gros, the Apotheosis of Saint Genevieve (1811–1834), is visible through the opening in the lowest cupola.

The groups around the painting, made during the Restoration of the Monarchy, represent Kings of France who played an important role in protecting the church.

[18] The four pendentives, or arches, which support the dome are decorated with paintings from the same period by François Gérard depicting Glory, Death, The Nation and Justice (1821–37).

The façade and peristyle on the east side, modeled after a Greek temple, features Corinthian columns and pedimental sculpture by David d'Angers, completed in 1837.

The original sphere from the pendulum was temporarily displayed at the Panthéon in the 1990s (starting in 1995) during renovations at the Musée des Arts et Métiers.

[23] The widely repeated story that the remains of Voltaire were stolen by religious fanatics in 1814 and thrown into a garbage heap is false.

[24] On 30 November 2002, in an elaborate but solemn procession, six Republican Guards carried the coffin of Alexandre Dumas (1802–1870), the author of The Three Musketeers and other famous novels, to the Panthéon.

In his speech, President Jacques Chirac stated that an injustice was being corrected with the proper honouring of one of France's greatest authors.

In January 2007, President Jacques Chirac unveiled a plaque in the Panthéon to more than 2,600 people recognised as Righteous Among the Nations by the Yad Vashem memorial in Israel for saving the lives of Jews who would otherwise have been deported to concentration camps.

The tribute in the Panthéon underlines the fact that around three-quarters of the country's Jewish population survived the war, often thanks to ordinary people who provided help at the risk of their own life.

Named as "Righteous among the Nations" or remaining anonymous, women and men, of all backgrounds and social classes, saved Jews from anti-Semitic persecution and the extermination camps.