Anna Deavere Smith in “Notes from the Field” (Joan Marcus)

NEW YORK –For helping kick her latest project into high gear, Anna Deavere Smith owes a debt to a surprising source: singer-songwriter John Legend.

“When I heard him say it,” she was explaining on a recent afternoon, “I realized there was a temperature rising in this country. It was then I knew it was in the zeitgeist.”

The “it” had to do with a remark Legend made at the 2015 Academy Awards that spoke to an issue that Smith was developing, as the theme of the new solo show she calls “Notes from the Field.” In his acceptance speech for Best Original Song, for “Glory” from “Selma,” written with Common and Che “Rhymefest” Smith, Legend talked about the enduring relevance of the movie, inspired by one of the seminal protest marches of the civil rights movement of the ’60s.

“We know that the voting rights that they fought for 50 years ago is being compromised in this country today,” the singer declared. But the words that hit the bullseye for Smith were contained in the impassioned Legend’s observation that there existed “more black men under correctional control today than were in slavery.”

It wasn’t that Smith required enlightenment on the subject of the inordinate stresses on men of color in America. She was already deep into the  research process for “Notes from the Field,” during which she would ultimately conduct 250 interviews across the country, in prisons, inner-city schools and on Native American reservations. The fact, though, that a performer at the center of popular culture was underlining the gravity of the topic for a global television audience represented, for Smith, a validation of a valuable sort and an incentive that fueled her belief in forging ahead.

Her exertions have resulted in one of the most compelling pieces she has assembled in the decades in which she has been perfecting the hybrid genre she pioneered: equal parts dramatic re-enactment, investigative stage documentary and analytical impersonation. The show is running at off-Broadway’s Second Stage Theatre and continues through this weekend. It’s the kind of intimately revelatory performance that allows theater to serve as a vital megaphone on a contemporary subject, with maximum emotional impact. And with any luck, theaters in other cities will get the chance to host it, too.

The hallmark of Smith’s style is her remarkable, protean ability to disappear into the real people she portrays, reproducing in verbatim monologues the points of views of interviewees from all walks of life. Though she’s played prominent on television (“Nurse Jackie”), she’s best known in the theater for the pieces she assembled around two flashpoint events in modern American race relations, a 1991 Brooklyn riot (“Fires in the Mirror: Crown Heights, Brooklyn and Other Identities”) and a violent disturbance in Los Angeles the following year, provoked by the acquittal of police officers after an assault on a black man, Rodney King (“Twilight: Los Angeles, 1992”).

Skillfully directed by Leonard Foglia, “Notes from the Field,” by Smith’s own reckoning, evolves out of an activist branch of the theater, as opposed to the type of more even-handed reportage that characterized her earlier works. On this occasion, Smith says, she does indeed have an agenda: exposing the deep flaws in American institutions that see people of color moving from failing schools to failing prisons. Inner-city educators and students, prisoners and politicians, Native American leaders and African-American protesters number among the 17 voices she summons over the 135 minutes of the monodrama. But it may be the comments Smith channels for us from  Sherrilyn Ifill, president of the NAACP Legal Defense and Education Fund, that best summarize the overarching theme of “Notes from the Field.” Ifill muses about having not been around for the historic early days of the civil rights movement — and then realizing that, given the ongoing spate of racially-charged incidents and tragedies in this nation, the work in that regard is far from over.

Reflecting on the themes of her show, Smith said: “The killing of Michael Brown changed the perspective of race in this country.” The 2014 shooting of Brown, an African-American, by a white police office in Ferguson, Mo., not only underscored for Smith that she was on an important trajectory with “Notes from the Field,” but that there was also an intensifying need for informed conversation. Indeed, Smith said, when “Notes from the Field” was produced last August at the American Repertory Theater in Cambridge, Mass., the show stopped at its midpoint at each performance, and Smith had the house lights turned up and encouraged audience members to talk about their reaction and own experiences. That piece of the production has been removed at Second Stage, but one imagines it could easily be reintroduced in other settlings.

“That’s always been a mission of the project,” Smith said of the plain talk “Notes from the Field has managed to generate. “And the project has always been a call to action.”

Notes from the Field, written and performed by Anna Deavere Smith. Directed by Leonard Foglia. Set, Riccardo Hernandez; costumes, Ann Hould-Ward; lighting, Howell Binkley; sound, Leon Rothenberg; projections, Elaine McCarthy; dialects, Amy Stoller. About two hours 15 minutes. Through Dec. 18 at Second Stage Theatre, 305 W. 43rd St., New York. Remaining performances sold out. Visit 2st.com or call 212-246-4422.