As the Supreme Court's Proposition 8 decision approaches, Morgan Freeman has lent his voice to a new pro-gay marriage ad for the Human Rights Campaign. Reuters

Morgan Freeman has lent his signature voice to a new pro-gay marriage ad for the Human Rights Campaign, or HRC. The 30-second spot, titled "A New Day for Marriage," features a montage of same-sex couples and historical images like the Statue of Liberty, the U.S. Constitution and Dr. Martin Luther King Jr.'s speech at the 1963 March on Washington.

"Freedom, justice and human dignity have always guided our journey toward a more perfect union," Freeman, who began his career in the mid-60s, says in the ad. "Now, across our country, we are standing together for the right of gay and lesbian Americans to marry the person they love. And with historic victories for marriage, we've delivered a mandate for full equality. The wind is at our back, but our journey has just begun."

HRC President Chad Griffin released a statement along with the ad, stating, "As we continue the march toward full equality in legislatures and the courts ... an equal future is no longer up for debate; the question now is how soon it will arrive."

The HRC is currently supported by a variety of celebrities, including Anne Hathaway, Scarlett Johansson and Brad Pitt, who donated $100,000 to the organization in March. According to its official website, the HRC is the largest civil rights organization working toward equaltiy for members of the gay, lesbian, bisexual and transgender community. With 1.5 million members, the organization aims to educate and develop inpactful campaigns.

Freeman is no stranger to political and humanitarian action. According to CNN, he narrated an ad for President Obama's reelection campaign in October and donated $1 million to pro-Obama super-PAC Priorities USA Action.

The 75-year-old is one of the founders of the PLAN!T now organization, which aims to assist those living in locations affected by severe storms. Freeman has also narrated promo spots for environmental organization One Earth.

Last year, the actor appeared in a one-night-only Broadway reading of Dustin Lance Black's play "8," about the trial to overturn California's ban on gay marriage.

Freeman's spot comes following the legalization of gay marriage in Maine, Maryland, Minnesota and Washington State, as well as the impending Dec. 3 Supreme Court decision on whether or not to review Proposition 8.