Senator Dianne Feinstein, the trailblazing Democratic power broker who served in the Senate for 30 years, died on Thursday night, according to a family member.

In recent years, Ms. Feinstein, 90, had suffered from frail health and memory issues that made it difficult for her to function alone and prompted calls for her to step down, which she consistently rejected.

Her condition had grown more acute over the past several months, after a bout with shingles that caused serious complications, including a case of encephalitis, and prompted her to begin using a wheelchair in the halls of the Capitol.

Ms. Feinstein’s long and very public decline shed a spotlight on the advanced age of members of Congress and particularly the Senate, where many continue to serve long after retirement age.

Her staff was being officially informed of her death at 9 a.m.

A spokesman for her Senate office did not immediately respond to a request for comment.

On Capitol Hill, where the Senate is racing to pass a temporary spending bill to avert a government shutdown at midnight on Saturday, her absence was unlikely to have an immediate impact. Her vote had not been expected to be determinative for passing that measure, which has broad bipartisan backing.