"Too often, our society seeks to label people by pinning them on the wall - straight, gay or in between," he wrote. "I don't categorise myself based on the gender of those I love. I had a half-century of marriage with a wonderful woman, and now am lucky for a second time to have found happiness.
"For a long time, I did not suspect that idea and fate might meet in my lifetime to produce same-sex marriage equality. My focus was on other issues facing our nation, especially advancing national service for all. Seeking to change something as deeply ingrained in law and public opinion as the definition of marriage seemed impossible.
"I was wrong, and should not have been so pessimistic."
A friend of Martin Luther King Jr's who served as John F. Kennedy's civil rights adviser, Wofford joined with Rep. John Lewis, D-Ga., during his single term in office to co-author the King Holiday and Service Act, legislation that would marry the national holiday with volunteerism.
In his essay, Wofford wrote that he once believed marriage equality to be impossible but eventually had a change of heart, using his past experience as a guide for the future.
"I had seen firsthand - working and walking with the Reverend Dr Martin Luther King Jr - that when the time was right, major change for civil rights came to pass in a single creative decade. It is right to expand our conception of marriage to include all Americans who love each other."
There are no details on the April 30 ceremony, but according to the essay, Wofford and Charlton plan to recite traditional marriage vows while joining hands and promising "to be bound together".