The Palais du Luxembourg, located within the park and now serving as the home of the French Senate, was built beginning in 1615 at Marie de Médicis's request. She acquired Hôtel de l’Luxembourg in 1612 (now known as Petit Luxembourg). Homesick for her native Florence, Marie tried to recreate its architecture and gardens (her former home Palazzo Pitti, and Giardino de Boboli) in central Paris. Her builders finished the Italianate palace in a mere five years. Marie gave Petit Luxembourg to Cardinal Richelieu in 1627. It did not work as expected – a feud with him made her time in the palace brief. Wielding great power, Richelieu (1585 – 1642) banished the Queen Mother on November 10, 1630 (period known as Days of the Dupes) to Cologne, where she died penniless in 1642. The palace went on to house a number of France's most elite nobility, and in later years, became a prison for those nobles awaiting the guillotine and then for Revolutionary Jacobin perpetrators. Imprisoned in the palace during the Revolution with her Republican husband, Beauharnais, the future Empress Josephine returned five years later to take up official residence with her second husband, the new Consul Napoleon Bonaparte. During WW II, the Nazis, who made it the headquarters of the Luftwaffe, occupied the palace. In 1852 the palace first served its current function as the meeting place for the Sénat, the upper house of the French parliament. The president of the senate lives in Petit Luxembourg, originally a conciliatory gift from Marie de Médicis to her nemesis Richelieu.

One of the loveliest spots in the Jardin is just east of the Palais, at the Fontaine des Médicis (1620), a Romantic grotto complete with a fish pond and baroque fountain sculptures. You can see here 19th C statues of the lovers Acid and Galatea about to be ambushed by jealous Cyclopes Polyphemus. Fountain Regard (built in 1807 on the corner of the rue de Vaugirard and rue Regard, sometimes called Leda fountain) was attached to the back of the Fountain Médicis in 1864.