The party was founded in April 1921, but soon banned under fascism, and was re-organized after World War II by Emilio Lussu, secretary for Southern Italy of the Action Party during the war, and other veterans from the Sassari brigade and anti-fascists, a social-democratic group of the Italian resistance movement. Lussu left the party in 1948 to found the short-lived Sardinian Socialist Action Party, which joined the Italian Socialist Party in 1949, along with many other PSd'Az members. Consequently, the PSd'Az started to cooperate with Christian Democracy and was quite a stable until the 1980s. The PSd'Az and the PSd'AzS won 10.5% and 6.6% respectively in the first regional election in 1949. After a decline in term of votes in the 1960s and 1970s, the party re-gained strength in the 1980s. Following these results, Sardist Mario Melis was President of Sardinia between 1984 and 1989 at the head of a five-party coalition composed also by the Italian Communist Party, the Italian Socialist Party, the Italian Democratic Socialist Party and the Italian Republican Party. This was the highest point in party history: the PSd'Az was represented in the Italian Parliament from 1983 to 1994, and Melis was a MEP for the Rainbow Group from 1989 to 1994. The party was affiliated to The Olive Tree during the 1996 general election. However, the party congress rejected a continuation of the alliance ahead the 2001 general election. In the 2004 Sardinian regional election the PSd'Az won 3.9% of the vote and 2 regional councillors. In the 2006 general election leader Giacomo Sanna, due to an electoral pact named Pact for the Autonomies, was a candidate of the Lega Nord for the Senate in Lombardy, but failed to get elected. The party ran by itself in the 2008 general election, winning a mere 1.5% in the Region. In the 2009 regional election the PSd'Az joined the centre-right coalition, provoking the split of the party's left that formed the Red Moors. Cappellacci won and the PSd'Az won 4.3% of the vote and four regional councillors plus one elected in Cappellacci's regional list. The Red Moors won 2.5% and one councillor. In the 2010 provincial elections the party was strongest in Nuoro, Sassari, Olbia-Tempio and Cagliari. In 2013 the PSd'Az broke with Cappellacci and the centre-right, but re-joined the coalition in time for the 2014 regional election. In the election Cappellacci was defeated and the PSd'Az won 4.7% of the vote and two regional councillors. In the run-up of the 2018 general election the party formed once again an electoral pact with the League, which presented itself as "Lega" all around the country. The alliance managed to get 10.8% of the vote and Christian Solinas, leader of the PSd'Az, was elected to the Senate, while Guido De Martini, a local activist of the LN, was elected to the Chamber. This marked the return of the PSd'Az to the Italian Parliament after 22 years. In August 2018 the party was suspended from the European Free Alliance because of its alliance with the League. In the 2019 regional election Solinas was elected President of Sardinia with 47.8% of the vote, while the PSd'Az won 9.9%.
Popular support
The party has failed to regain the electoral support it enjoyed upon its foundation. The party has been mostly marginal in the Sardinan political scene since World War II and this marginalisation has increased with the establishment of a bipolar political system in the 1990s. Eve Hepburn, a political scientist, has suggested the reasons for the party's failure in getting electoral success and influence can be identified in different factors that include its ideological incoherence, its consequent erratic choices of coalition partners, its inability to adapt to multi-level politics. The electoral results of the PSd'Az in regional and Chamber of Deputies elections in Sardinia since 1946 are shown in the chart below. For 1953 only the regional election's result is shown. In the general elections of 1972, 1976, 1979 and 2006 the party did not run lists for the Chamber of Deputies.
