"I believe in trying to work with people," he said. "It will be hard. It’s going to be very difficult. I don’t see this president-elect as a legitimate president.”
Lewis also said he believes Russia President Vladimir Putin helped elect Trump.
Related: Pastor of MLK’s church: Trump is a ‘small man’ for attacking Atlanta
“I think it was a conspiracy on part of the Russians and others to help him get elected," he told MSNBC. "That’s not right, that’s not right. That’s not fair. That’s not the open democratic process."
Lewis has become one of the most vocal critics of Trump, vowing to resist his presidency. He testified this week against U.S. Sen. Jeff Sessions, R-Ala., Trump's nominee to be attorney general, and has urged Democrats to unite against his policies.
Related: Georgia Republicans struggle to defend Trump’s attack on Lewis
His civil rights legacy gives him a prominent pulpit. He was chair of the Student Nonviolent Coordinating Committee in the early 1960s and led countless sit-ins and protests. An ally of King, Lewis was an architect of the March on Washington in August 1963 and was beaten so badly during the 1965 Selma to Montgomery march that his skull was fractured.
The Democrat's district includes parts of Fulton, DeKalb and Clayton counties - and most of the city of Atlanta - as well as Brookhaven, College Park, Decatur and Morrow. The district has several of Atlanta's most prominent gems, including Hartsfield-Jackson Atlanta International Airport, the King Center and the federal Centers for Disease Control and Prevention.
Related: The 12 times Congressman John Lewis broke the internet
And it has the bulk of Georgia's higher education institutions: Emory University, Clark Atlanta University, Morehouse College, Georgia Tech and Georgia State University are all in the 5th Congressional District. It is also where many of the state's Fortune 500 companies are based, including Coca Cola Co., Southern Co. and Delta Air Lines.
It is also one of the most diverse districts in the South. Census data show it is about 58 percent black and 33 percent white, along with a growing Hispanic population. The district has an 8.2 percent unemployment rate and the median household income for residents is about $48,000.
Here are Trump's tweets: