Yes, MARSHALL is a Scrabble word!

Letter values in Scrabble US: M 3, A 1, R 1, S 1, H 4, A 1, L 1, L 1.

Is it a valid word?

MARSHALL is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

United States actor (1914-1998)
United States general and statesman who as Secretary of State organized the European Recovery Program (1880-1959)
United States jurist; as chief justice of the Supreme Court he established the principles of United States constitutional law (1755-1835)
(in some countries) a military officer of highest rank
a law officer having duties similar to those of a sheriff in carrying out the judgments of a court of law

Also: e. g. marshall, george marshall, george catlett marshall, john marshall.