U.S. Rep. Michael Capuano, facing a primary challenge from Boston City Councilor Ayanna Pressley, is hosting a town hall forum in Roxbury on Saturday with civil rights icon U.S. Rep. John Lewis.

A black civil rights activist who protested racist Jim Crow segregation with lunch-counter sit-ins before his election to represent Georgia in Congress, Lewis will join Capuano at the Twelfth Baptist Church at 10 a.m. Saturday, Capuano's campaign announced. Lewis has already endorsed Capuano's re-election bid, calling the former Somerville mayor "a champion and fierce advocate for those who have often been forgotten or left behind."

Pressley, the first African-American woman elected to the Boston City Council, is challenging her fellow Democrat to represent the majority-minority congressional district that includes Chelsea, Everett, Randolph, and Somerville, as well as swaths of Boston, Cambridge and Milton.

Roxbury will not be Lewis' only stop in Massachusetts. On Friday night, he will be the guest at a Worcester fundraiser to support U.S. Rep. James McGovern. On Sunday, Lewis is scheduled to give the keynote address at Boston University's commencement. He will also speak at Harvard's graduation ceremony May 24.

The Boston Musicians Association, with more than 1,600 members, endorsed Pressley on Thursday. Last week, At Large Boston City Councilor Annissa Essaibi-George endorsed Pressley, saying: "Before I was elected to the Boston City Council, I didn't fully appreciate the impact of Councilor Pressley's voice and leadership."