It was a baby who convinced Tracy “Twinkie” Byrd that she wanted to become a casting director.

While working at the Manhattan offices of advertising agency DMB&B, where Byrd was a legal secretary with a self-described outsized personality, a baby came in to audition for a Pampers spot and wouldn’t leave her lap; she was asked to hold the child for the casting session. Enchanted by what she saw, she enlisted the casting director as a mentor.

Now, the former casting assistant for TV shows like “Moesha” and casting director for films like “Stomp the Yard” and “Notorious” will see the latest pic on which she worked, the Sony remake of “Sparkle,” hit theaters Aug. 17. A musical drama about the travails of a Supremes-like ’60s vocal trio starring former “American Idol” winner Jordin Sparks, Byrd says that being an African American gave her an insight into the film.

“In the script, there are certain terms and phrases that are used in the African-American community that some other people wouldn’t know or understand necessarily,” says Byrd, such as “red” (for black people with red hair or a light complexion and freckles) and “blue” (for the very dark-skinned).

But she admists that there were many aspects completely alien to her experience.

“I’ve never had to share my room,” recalls Byrd, seated in a cafe near her Studio City home. “My parents have been married for 51 years. I grew up in a house with two cars and a dog,” in a predominantly Italian-American neighborhood in Sheepshead Bay, New York. “But I do know about overcoming adversity.”

The problem, she says, was not skin color, but her dominant personality.

“It was too much for most of my (early) jobs, so I always got fired,” says Byrd. Working as a legal secretary, she says she had no problem getting a job, because she could type 95 words a minute. “But I talked too much on the phone and I’d draw people in, so everybody would want to be at my desk.”

As a casting director, however, personality can pay dividends.

Over the next few years, Byrd interned for casting agencies at night while holding down day jobs with Essence Magazine and publicist Terrie Williams. Eventually, she established herself in musicvideo and commercial casting, working with directors such as Brett Ratner, Mary Lambert and Tim Story, but it wasn’t enough — she wanted to work in film and TV.

In 1997, she moved to L.A., where she worked on “Moesha” while continuing to cast videos. Eager to prove she had what it takes to do movies, in 2002, she offered her services to students at AFI, and wound up casting a long string of short films.

In 2005, she was hired by her brother, director Jeffrey W. Byrd, to serve as the casting director on his feature “King’s Ransom,” which led to a slew of other bigscreen assignments including 2007’s “Stomp the Yard,” 2009’s “Notorious” and 2011’s “Jumping the Broom,” helmed by “Sparkle” director Salim Akil.

Although most of her feature credits could be characterized as being in black-themed films, Byrd, who’s casting a one-hour drama for BET starring Gabrielle Union, titled “Miss Mary Jane,” also served as casting director for “Filly Brown,” which features a preponderance of Latino roles. A few month earlier, participating in a post-screening discussion of that film in Los Angeles, she found herself in the middle of a diversity issue.

Actor Edward James Olmos threw out a disturbing statistic: Latinos represent more than 20% of the U.S. population , but they are seen in less than 2% of the images seen on film and TV. Then, touching Byrd on the arm, he added that while African-Americans are only 12% of the population, they are seen in 17% of film and TV images.

Byrd was already uncomfortably aware that apart from the moderator, actor Harry Lennix (“Ray,” “A Beautiful Soul”), she was the only non-Latino onstage, and one of the few African-Americans at the event. Finally, an audience member asked the elephant-in-the-room question: How is it that a black woman like Byrd was chosen to cast this overwhelmingly Latino project about a Los Angeles street poet (Gina Rodriguez) on the rise?

Byrd told them the reason was simple.

“They needed a great casting director, and I’m great at it,” Byrd said. “It doesn’t matter what your ethnicity is. I can tell truth in performance.”

Indeed, Byrd says she is looking to branch out.

“It’s my career,” she says. “There are projects I want to do and stories I want to tell.