Short answer: no.
If you ever find yourself arguing with conservatives about Martin Luther King Jr. (and if you’re a black liberal this always happens), inevitably they will assert that King was a Republican. This is often based on a claim from Alveda King, his niece, a conservative who has been disavowed by most of the rest of the King family, who are on the left of politics, as was Dr. King.
Alveda King has herself retracted this claim. From a press release she sent out in 2013:
I have few regrets in my life. At the top of the list is the demise of two children in my womb, and one miscarriage. Next to that, I regret having said to a group of peers that my Uncle M. L. (Dr. Martin Luther King, Jr.) was a Republican. My Grandfather, Dr. Martin Luther King, Sr. was a registered Republican. Uncle M. L. was an independent. I assumed that since Granddaddy was a Republican, Uncle M. L. was too. After all, before the election of President John F. Kennedy, the majority of African American voters were Republicans. Granddaddy convinced a large block of Blacks to vote for President John Kennedy after he helped to get my uncle out of jail during those turbulent days. Uncle M. L. tended to vote Democrat, but remained independent because he found weaknesses in both parties.
King’s mission was beyond the politics of the Democratic Party, and during his time as an activist he was forced to build a coalition from both parties –something that would have been hampered if he tied himself down with domestic politics. King relied on liberal Republicans and was often opposed by conservative Southern Democrats. Why would he have written off either party completely when his goal was legislation that had to be passed with support from both sides? (Details here on what that legislation eventually ended up looking like with support from Democrats and Republicans, signed into law by a Democratic president from the south).
Here is a quote from Martin Luther King Jr. about both political parties:
“Actually, the Negro has been betrayed by both the Republican and the Democratic party. The Democrats have betrayed him by capitulating to the whims and caprices of the Southern Dixiecrats. The Republicans have betrayed him by capitulating to the blatant hypocrisy of reactionary right wing northern Republicans. And this coalition of southern Dixiecrats and right wing reactionary northern Republicans defeats every bill and every move towards liberal legislation in the area of civil rights.” [The Papers of Martin Luther King, Jr: Symbol of the Movement, January 1957 – December 1958. University of California Press. p. 84]
Martin Luther King Did Not Publicly Endorse Either Party. As leader of the Southern Christian Leadership Conference, Dr. King did not publicly endorse candidates from either the Democratic or Republican parties. He said, “I don’t think the Republican party is a party full of the almighty God nor is the Democratic party. They both have weaknesses … And I’m not inextricably bound to either party.” [The Papers of Martin Luther King, Jr: Symbol of the Movement, January 1957 – December 1958. University of California Press. p. 364]
Martin Luther King Said “I Always Voted The Democratic Ticket.” In October of 1956 in a letter to a civil rights supporter, King said that “In the past I always voted the Democratic ticket” [The papers of Martin Luther King, Jr.. University of California Press. p. 384]
Martin Luther King Voted For JFK In 1960, Would Have Voted For Him In 1964. In his autobiography, King said that in 1960 he voted for John F. Kennedy because he “felt that Kennedy would make the best president.” He also wrote, “Had President Kennedy lived, I would probably have endorsed him in 1964.” [King, Jr., Martin Luther; Carson, Clayborne (1998). The Autobiography of Martin Luther King, Jr.. Hachette Digital. p. 187]
Martin Luther King Supported Lyndon Johnson in 1964, Attacked Conservative Republican Barry Goldwater, Said GOP Pandered To Racists At Convention. From Dr. King’s Autobiography:
The Republican Party geared its appeal and program to racism, reaction, and extremism. All people of goodwill viewed with alarm and concern the frenzied wedding at the Cow Palace of the KKK with the radical right.
While not himself a racist, Mr. Goldwater articulated a philosophy which gave aid and comfort to the racist. His candidacy and philosophy would serve as an umbrella under which extremists of all stripes would stand. In the light of these facts and because of my love for America, I had no alternative but to urge every Negro and white person of goodwill to vote against Mr. Goldwater and to withdraw support from any Republican candidate that did not publicly disassociate himself from Senator Goldwater and his philosophy. [King, Jr., Martin Luther; Carson, Clayborne (1998). The Autobiography of Martin Luther King, Jr.]