He wasn’t a socialist (I think?) so he wasn’t a leftist. And he wasn’t a conservative obviously.
https://www.commondreams.org/views/2019/01/21/11-most-anti-capitalist-quotes-martin-luther-king-jr
That has a lot of his 1967 quotes. He isn’t a communist but he’s more on the demsoc side of the socdem-demsoc divide. I think his problem there is that he grew out of liberation theology and the black churches formed a big chunk of his base. They’re otherwise generally a conservative community outside of the narrow lines of the civil rights movement’s social liberation. The Black Panthers and similar groups had a monopoly on anything more radical than that and he was committed to non-violence. The Poor People’s Campaign strikes me as a more comprehensive Bernie Sanders platform: https://www.crmvet.org/docs/68ebr.htm
The Southern Christian Leadership Conference, architects of the Poor People’s Campaign, have outlined 5 requirements of the bill of economic & social rights that will set poverty on the road to extinction:
- A meaningful job at a living wage for every employable citizen.
- A secure and adequate income for all who cannot find jobs or for whom employment is inappropriate.
- Access to land as a means to income and livelihood.
- Access to capital as a means of full participation in the economic life of America.
