Arrested by the ascendant communist authorities in 1947 as a result of the Tămădău affair, he was convicted of treason in a show trial and sent to Sighet Prison, where he died six years later.

Maniu joined the Romanian National Party of Transylvania and Banat (PNR), became a member of its collective leadership body in 1897, and represented it in the Budapest Parliament on several occasions.

In May 1919, during the Hungarian–Romanian War, he accompanied King Ferdinand I and Queen Marie on a visit to Alba Iulia, Oradea, and Carei, and a meeting with the frontline troops at Békéscsaba.

[1] After the creation of Greater Romania, the PNR formed the government in Bucharest—a cabinet led by Al. Vaida-Voevod and allied with Ion Mihalache's Peasants' Party.

Despite its success in elections, the PNȚ was blocked out of government by the Royal Prerogative of King Ferdinand, who had preferred to nominate Brătianu, Averescu, and Prince Barbu Știrbey.

In 1937, Maniu agreed to sign an electoral pact with the Iron Guard's Corneliu Zelea Codreanu, in the hope that this would block the monarch's maneuvers.

The king instead sought an agreement with other members of the political class, including the National Liberal Ion Duca and the former PNȚ politician Armand Călinescu, while clamping down on the Iron Guard—leading to a wave of similar actions in reprisal.

He remained an opponent of Antonescu, a view which he balanced with his adversity towards the Soviet Union, and joined the plotters of the pro-Allied royal coup of 23 August 1944, while expressing his resentment of the Romanian Communist Party (PCR) involvement.

"This man, in his seventies, who holds no meetings, makes no public speeches, publishes no articles, possesses no wealth, and is not allowed to answer one single calumny hurled against him, seems to have filled the Government with fear."

After the fall of Communism in 1989, some authors went as far as to claim that the PNȚ had actually won the election but was denied victory because of widespread electoral fraud on the part of the pro-Communist Petru Groza government.

On November 12, 1998, the High Court of Cassation and Justice ordered the rehabilitation of Maniu and removed the additional punishment of confiscation of property, pronounced in 1947.

"[8] A bust of Maniu was placed in Bucharest's Revolution Square, in front of the building of the former Central Committee of the Romanian Communist Party (from where Nicolae Ceaușescu and his wife fled by helicopter on December 22, 1989).