After an initial trip to his ancestral Lithuania and Belarus in 1990 (during which he negotiated an agreement[12] enabling Lithuanian students to enroll in Oxford Jewish studies courses), Katz pioneered the mounting of in-situ post-Holocaust Yiddish dialectological and folkloristic expeditions in Eastern Europe.

In early 2013 he began posting clips from his interviews of Boro Park Yiddish speakers gleaned from his return trips to his native Brooklyn.

Fragn fun yidisher stilistik" (Oxford, 1993),[15] both of which aimed to enhance the teaching of Yiddish as a vibrant language both spoken and for new literary and academic works, even if in (and for) small circles.

Katz, taken aback by the poverty he found among the last aged Yiddish speakers in Eastern Europe (many of them "flight survivors" who survived the war by fleeing to the Soviet Union, hence not eligible for aid under the narrow definition of "Holocaust survivor"), alerted the wider world to the issue in a 1999 op-ed[32] in the Forward, which was cited by Judge Edward R. Korman in the Swiss Banks settlement[33] in the U.S. District Court in 2004.

Katz began to work closely with the American Jewish Joint Distribution Committee (JDC) on these issues, and he helped the founders of the Survivor Mitzvah Project by a group based in Santa Monica, California.

In 2018, to honor the 100th anniversary of the establishment of the modern Lithuanian republic in 1918, he initiated a new online Yiddish "mini-museum" stressing interwar Yiddish-Lithuanian multicultural and bilingual life.

[40] After observing the Vilnius scene for years, Dovid Katz began in 2008 to publicly challenge the double genocide theory of World War II and the accusations against Holocaust survivors who survived by joining the Jewish partisans.

[41] When, in May 2008, Lithuanian prosecutors launched investigations of two more elderly Holocaust survivors, Fania Yocheles Brantsovsky and Rachel Margolis, Katz embarked on a new activist phase of his life.

[64] His professorship at Vilnius University was terminated after eleven years in 2010 after he published several articles critical of Lithuanian prosecutors' campaign against Holocaust survivors who joined the partisans.

In 2016 was appointed professor (on an adjunct basis) at Vilnius Gediminas Technical University (VGTU), in the Department of Philosophy and Cultural Studies, where he taught courses in Creative Writing and Ethics, until taking leave in 2020.

[75] Katz's work on the Holocaust in Lithuania and related antisemitism issues was among the subjects of a 2010 BBC world service program by Wendy Robbins,[76] and a 2012 Australian documentary film by Marc Radomsky and Danny Ben-Moshe.

On the subject of free speech, he has been a vocal critic of Lithuania's 2010 law[95] forbidding the denial or trivialization of Soviet and Nazi genocide, which he believes, in agreement with Leonidas Donskis,[96] to constitute criminalization of debate.

When the law was applied to a left-wing politician with whom he disagreed wholly on the 1991 events in question, Katz nevertheless felt it important to speak out for free speech,[97] and, in a reply to Rokas Grajauskas in Lithuanian Foreign Policy Review[98] made clear his view that objecting to Holocaust Obfuscation in no way signifies reluctance to expose Stalinist crimes.

[108] In the spring of 2011, Katz was Jan Randa Visiting Scholar at the Australian Center for Jewish Civilization (ACJC) at Monash University in Melbourne where he lectured on both Yiddish Studies and Holocaust issues.

He has worked to define the new and "nuanced" elitist East European antisemitism and its success in attracting unsuspecting westerners to help provide political cover.

He participated in the April 18, 2013 seminar on "Red equals Brown issues"[112] in Berlin, and a May 27–28, 2013 conference in Riga on Holocaust commemoration in post-communist Eastern Europe.

Germany's Federal Agency for Civic Education (FACE, German: Bundeszentrale für politische Bildung (bpb)) hired Katz in 2021 to classify today's historical significance of eighty years since Operation Barbarossa (Germany's attack on the Soviet Union) where the Nazis (prior to the "Wannseekonferenz") experienced that Holocaust in the Eastern Territories ("the Bloodlands") was "doable", not least because nationalist leaders in the Baltic States and Ukraine, hated the Soviet Union and Russia much more than collaborating with Nazis.

Bandera, Norieka and Skirpa whose ideas were responsible for mass killings of Jews and Poles, still today (2023) are honored by street names and plaques as freedom fighters in their respective countries.

Unexpectedly for many in his circles, he became, in 2015, a staunch opponent of plans to locate a national convention center on the grounds of Vilnius's 15th century-origin old Jewish cemetery.