Simonescu joined an editorial team headed by senior scholars Ioan Bianu and Nicolae Cartojan, and, in the 1930s and 1940s, became a major contributor to the collection and publication of old Romanian literature; he was also Cartojan's disciple, though the two disagreed on a parallel project, namely the publication of Mihail Kogălniceanu's collected works, with Simonescu favoring, and eventually putting out, a topical selection of Kogălniceanu's social-themed essays.

Having obtained a professorship at Iași University during World War II, Simonescu joined the Social Democratic Party in the late 1940s, and was briefly employed as a department head by the Education Ministry.

By 1956, he could return with more editions of Kogălniceanu, and more secretly networked with other old-regime intellectuals, including G. T. Kirileanu; they ensured the preservation and eventual resumption of cultural research that went against the official interpretation of Marxism–Leninism.

He is widely seen as responsible for the definitive Kogălniceanu edition, while also contributing studies of ancient literature, including romances and rhyming chronicles, with additional returns to both bibliography and folkloristics.

Simonescu was additionally instrumental in the rediscovery of historical writings by Balthasar Walther, though also criticized for allowing communist censors to remove a fragment referencing Michael the Brave's antisemitism.

[7] His early education was completed in Câmpulung and Pitești, where, according to his own recollections, he became more disciplined and began modelling himself on his teachers, especially Alexandru Bărcăcilă and Mihai Mihăileanu, who taught him Latin.

He was initially drawn by classical scholarship, in the same class as Alexandru Graur, but was put off by professor Dumitru Evolceanu, whose teaching methods he regarded as superficial; he was instead impressed by Iuliu Valaori, who introduced him to Latin literature.

[12] "Student Dan I. Simonescu, originally from Câmpulung" was cited as an informant by the folklorist Ioan Aurel Candrea, referencing a Muscel legend which claimed that brigand Gheorghe Fulga had escaped from jail using a miraculous week called iarba fiarelor.

[17] Collaborating with senior bibliographers such as Bianu and Cartojan, who informed his approach to historiography, he became fascinated with incunabula; on behalf of the academy, he was editor of the well-received third-volume of Bibliografia românească veche ("Old Romanian Bibliography"), which came out in 1936.

[22] Cartojan, alongside Bianu, Russo and others whom he met at the academy, gave him living proof that "one cannot complete a thorough paper without sacrificing one's hours of leisure and entertainment, one's personal and family interests, one's health and friendships.

[23] Spurred on by Cartojan,[15] he attended specialized courses at Athens and Istanbul (1934), followed by an extended stay as a visiting scholar at the Bibliothèque nationale de France in Paris (1937).

[19] Historian Emil Lăzărescu took a reserved view, noting that Simonescu had failed to reveal some of his sources, and that the paper contained too few direct citations from Georgiakis.

As part of this maneuver, Giorge Pascu was forced to resign from the Bucharest University's Chair of Old Literature; Cartojan tried to get Simonescu nominated for that position, but failed to obtain relevant support.

[10] Alongside Ion C. Chițimia and Alexandru Rosetti, and under Cartojan's guidance, he began publishing a corpus of old Romanian literature, of which only three volumes came out (two in 1942, and the third, namely the German Chronicle of Stephen the Great's reign, in 1944).

[33] Simonescu was the first expert to investigate the collection of Romanian manuscripts that scholar Moses Gaster had bequeathed to the academy, publishing his results in a 1940 issue of Viața Romînească.

It detailed the old chroniclers' emancipation from the standards imposed by Constantine Manasses, dwelling on Grigore Ureche and Miron Costin's effort to distinguish propaganda and calumny from historical truth.

In February 1945, Simonescu was lecturing at the newly formed Romanian Society for Friendship with the Soviet Union (ARLUS) of Bucharest, discussing Dimitrie Cantemir's activity in the Russian Empire.

[43] He was elected a regional delegate of the Democratic Students' Front,[44] and, at a congress held on June 18, 1946, joined the national executive board of the Union of Teachers' Syndicates.

As recalled by Anghelescu, who was at a time a student of literature, the senior scholar had been barred from teaching by the communist censors—a lesser punishment than those reserved for other specialists, whose work was entirely purged from academia.

[52] As noted in 1977 by Ursu, the "demands of the cultural revolution in our country" also led Simonescu to participate in popular education, with lectures at the Bucharest people's university.

[17] In 1955, Simonescu curated Kogălniceanu's selected works for the Biblioteca pentru toți collection, with a preface which depicted the author "as a thinker of progressive outlook, who never went down the reactionary path taken by the bourgeoisie".

[55] In mid-1957, he was allowed to publish in the historical magazine Studii și Materiale de Istorie Modernă, earning praise for putting out Kogălniceanu's first-ever complete bibliography.

It was panned by linguist Ion Gheție, who argued that Simonescu had merely put together a collection of words which modern Romanian never adopted, such as "ill-adapted neologisms" and samples of Kogălniceanu's preference for the Moldavian dialect.

[1][10] As literary critic Ion Simuț cautions, Simonescu actually shared credit with a team of historians, including Alexandru Zub and Dan Berindei, but was widely regarded as a "coordinator of sorts" after prefacing the first Kogălniceanu volume, in 1974.

[2] One year later, he wrote and published Cronici și povestiri românești versificate ("Romanian Chronicles and Stories in Verse"), which included detail on the mourning song for Constantin Brâncoveanu and its transition into Wallachian folklore.

Held at Dalles Hall of Bucharest, it had topical contributions by various guest speakers, including Buluță, artist Marcel Chirnoagă, and historian Ludovic Demény.

[78] The scholar also made a return to folkloristics with an introductory study to Rădulescu-Codin, published in 1986 as part of Editura Minerva's folk-literature reader (Literatură populară).

As he noted in his correspondence, his re-familiarization with Muscel's traditions required him to read the works of Mihail M. Robea; he also relied on biographical material sent to him by Ion Cruceană of Pitești.

[2] Simonescu was still regularly writing at the time, and had prepared for print a paper on Ovid Densusianu; as argued by Anghelescu, his work in comparative literature had reached its peak with additional studies on 18th- and 19th-century translators, from John Caradja to Cezar Bolliac, as well as with his opening up discussions about Western influences on 17th-century Romanian culture.

[66][67] Simonescu, Buluță and Iurie Colesnic are also credited as the authors of Scurtă istorie a cărții românești ("A Short History of the Romanian Book"), put out by Editura Demiurg in 1994.