Formerly The Partnership for a Drug-Free America - and perhaps best known for the "this is your brain on drugs" ads of the 1980s and 1990s - the organization launched its new name and announced Gilbert's role Thursday.
"I come at the issue of addiction from so many angles," Gilbert, 46, said in an interview.
In addition to being a mother and stepmother of four with a parent's interest in prevention, Gilbert has had her own struggles with alcohol and drugs.
"I myself am a recovering alcoholic, six years sober," the former "Little House on the Prairie" star said, adding that "as a young teen in the 1980s, I more than dabbled in drugs and alcohol."
Steve Pasierb, president of the New York-based partnership, said that although it has worked with celebrities on previous campaigns, the organization has never had a long-term celebrity spokesman before.
"We were trying to find these voices that don't bring celebrity for the sake of celebrity, but bring along credibility," he said. "Melissa is in recovery herself and she's got kids, it was a perfect combination of our wanting to have a real relationship and her wanting to have a real relationship."
On the re-branding effort, Pasierb said the organization's new name better reflects the role it can play in the lives of today's parents.
"What we were hearing a lot from parents was that they appreciated the prevention stuff, but when it came to their kid coming home drunk for the first time, or getting high for the first time there was no one out there," Pasierb said. "We want to be the first-aid kit of this issue."
He said he hopes the Partnership at Drugfree.org name will avoid the misperception that the nonprofit group is a government organization or is primarily involved in advocating about drug policy, he added.
He said the organization's website, drugfree.org, offers parents advice in several distinct areas: "my kid hasn't used," or prevention; "my kid is dabbling," or intervention; "my kid has a problem," or treatment; and "how life goes forward," or recovery.
The organization also supports community-based drug prevention and education efforts.
As a parent, Gilbert said she appreciates the information on the partnership's site, saying she "wanted to be able to be aware of what's out there" today, so she can talk to her 15-year-old son about drugs.
Gilbert added that parents her age and younger often face different challenges than earlier generations of parents faced when discussing drugs with their children, because "we can't actually say to our children, you shouldn't do it, because I never did," she said. "It's a whole different conversation."
In spite of her personal experience with drugs, when a member of her family was having problems, she failed to notice the signs.
"I had no clue that he was having issues with cocaine, and that was my drug," she said, adding "it can be so isolating," to have a family member struggling with addiction.
Gilbert believes the ability to research online anonymously at drugfree.org will comfort parents who don't know who to talk to when dealing with addiction in their families.
The "Little House" star said she hopes that hearing from someone like her, who grew up on their TV sets, will help today's parents avoid this isolation.
"I'm hoping that they'll come away with ... the thought that the stigma of being a parent with a child who is going through addiction issues is nonexistent," Gilbert said, "because it can happen to anyone."