Take a back seat

This phrase has a straightforward and literal derivation. It alludes simply to the back seats, of a coach, a theatre, a gaming table etc., being less prominent than the others. It originated in the USA in the mid 19th century. As we might expect, the earliest uses of the phrase merely refer to people sitting at the back.

An early example from The Washingtonian, July 1845 seems to be moving part of the way from a literal to a figurative sense:

He took a seat at the [poker] table, and they dealt him a hand. It wasn’t long before… he was broke, and compelled to take a “back seat.”

The use there of back seat in quotation marks suggests that the expression had a meaning beyond the position of the seat. The context of the citation suggests that those who weren’t in a position to make a bet sat at the back.

The first use that I can find of an unambiguously figurative use of the phrase, that is, one where no actual seat is occupied, comes from The Daily Wisconsin Patriot, May 1859:

“The despised foreign born slave – the much hated and often cursed ‘Irish,’ ‘Dutch’ and ‘Norwegians,’ must take a back seat in the exercise of all the foregoing announced privileges [voting, jury duty etc.] – no man of foreign birth can vote until two years after he shall have received his full papers.”

See also; back seat driver.