D’Alesandro died Sunday at his Baltimore home of complications from a stroke, his family said.
"My husband Paul and our entire family are devastated by the loss of our patriarch, my beloved brother, Thomas D'Alesandro III," Pelosi said in a statement.
Politics runs in the family.
Father Thomas D’Alesandro Jr. served in the U.S. House of Representatives from 1939 to 1947. He also served 12 years as mayor of Baltimore.
Nancy is the first woman to serve as speaker of the House.
"Tommy was the finest public servant I have ever known," Pelosi said in a statement. "He profoundly believed, as did our parents, that public service was a noble calling and that we all had a responsibility to help others."
D’Alesandro served as mayor of Baltimore from 1967 to 1971. He led the city during the race riots of 1968.
"As the city's 42nd mayor from 1967 to 1971, he will long be remembered for his leadership in divisive times, and for his efforts to root out discrimination and rebuild the city he loved," Maryland Gov. Larry Hogan said in a statement.
He left after one term. He went into private practice as a lawyer.
Current Baltimore Mayor Bernard C. Jack Young praised D'Alesandro's commitment to the city during difficult times.
"He guided the city at a tumultuous time and made important strides while in office like creating summer recreation programs for youth, removing racial barriers in employment and education and laying the groundwork for what would become the world-famous Inner Harbor," Young said in a statement.
D'Alesandro is survived by his wife, Margaret; children Thomas, Dominic, Nicholas, Patricia and Gregory; 10 grandchildren "whom he adored" and 3 great-grandchildren, The Washington Post reported.