The day she got a lucky break, the kind budding New York actors dream about, Harmony Santana was living in a Harlem shelter for homeless youth and contemplating what she stood to lose by starting to live as a woman permanently.

She was 19 then, in 2010, when a director spotted her on the street and asked her to audition for a role in “Gun Hill Road,” the first film in which an openly transgender actor played a transgender character in a major role. When she accepted the part, Ms. Santana, then in the early stages of transitioning, was apprehensive about coming out so publicly.

“It was either help women like me and put awareness out there, or I could just live my life as a normal girl,” she said. “I chose to make a difference.”

Her breakout role became part of the recent and remarkable rise of visibility of transgender Americans, a segment of the population that has begun asserting control of its narrative after decades of being widely misunderstood and disparaged. With scores of people documenting their transitions on YouTube, popular television series depicting transgender characters with nuance and an ever growing number of ordinary Americans coming out, the community is starting to shed its stigma.