Is the word there'd a pronoun or a verb?

The contraction"there'd" is a shortened form of "there would" or "there had".
The contraction "there'd" is a combination of the pronoun"there" and the verb "would" or "had".

The contraction "there'd" functions as a subject and an auxiliary verb in a sentence or a clause.

Examples:
I thought there would be more time between flights.
Or, I thought there'd be more time between flights.

There had been a candy shop in this space before the taco stand.
Or, There'd been a candy shop in this space before the taco stand.