[3] He completed his mandatory military service in 1978–1979 within a unit troops answering to the Securitate, Communist Romania's secret police, ending as a 2nd Lieutenant and later recalling that his instruction was purely in regular combat.

[1] During this period, he would sometimes travel to villages for trials; according to Silviu Curticeanu (a former high-ranked Communist), these were held before packed audiences forcibly brought there, with judges usually selected based on political criteria often handing out especially harsh sentences for the "preventive-educational" effect these were supposed to have.

Continuing at the ministry, from 1998 to 2000 he headed its general law and consular directorate; among his attributes was that of chief negotiator for bilateral treaties on borders and minority rights.

[4] At the 2004 election, which the PSD lost, he won a Senate seat, and chaired that body's defence, public order and national security committee.

[8]) Diaconescu reluctantly agreed to run for Mayor of Bucharest in June 2008, promising a doubling of the minimum monthly salary and an additional pension payment per year.

[14] Later, in an interview, he added that improving relations with Russia and China was also on his agenda, as well as having the EU focus on energy security.

[18] Additionally, he had to deal with the sometimes tense situation faced by Romanian citizens living in Italy[19] and the United Kingdom.

[21] In February 2010, Diaconescu sought election as PSD president, but withdrew from the race several hours before the party congress that would decide the winner opened.

Subsequently, journalist Floriana Jucan alleged that Diaconescu had been subject to round-the-clock surveillance for ten days prior to the congress, and that party colleagues had carried out the monitoring in order to blackmail him.

Initially sitting as an independent in Gabriel Oprea's group,[22][23] he followed the latter into the newly founded UNPR, being elected honorary president in May.

[25][26] After Boc and his cabinet resigned the following month, Diaconescu was retained in his post by incoming prime minister Ungureanu.

[42] His eleven-month term ended when supporters of former PMP leader Eugen Tomac convened a party congress.