Republicans have chosen Senator Katie Britt of Alabama to deliver their response to President Biden’s State of the Union address on Thursday night, turning to one of their youngest members of Congress to burnish the image of their aging, male-dominated party and draw a contrast with a president nearly 40 years older.

Ms. Britt was sworn in last year after being endorsed by former President Donald J. Trump, whom she has endorsed in his 2024 campaign. She is the first elected female senator from Alabama and, at 42, the youngest Republican woman to have been elected to the Senate. She was born while Mr. Biden, 81, was serving his second term there.

“The Republican Party is the party of hard-working parents and families, and I’m looking forward to putting this critical perspective front and center,” Ms. Britt said in a statement last week. “There is no doubt that President Biden’s failed presidency has made America weaker and more vulnerable at every turn. At this decisive moment in our country’s history, it’s time for the next generation to step up and preserve the American dream for our children and our grandchildren.”

Speaker Mike Johnson noted in announcing her selection that Ms. Britt is the “only current Republican mom of school-age kids serving in the Senate.”

Senator Mitch McConnell, Republican of Kentucky and the minority leader, said: “Senator Katie Britt is an unapologetic optimist, and as one of our nation’s youngest senators, she’s wasted no time becoming a leading voice in the fight to secure a stronger American future and leave years of Washington Democrats’ failures behind.”

In choosing her, Republicans were saddling Ms. Britt with a tradition so difficult to perform well that it has come to be seen as somewhat cursed: delivering the opposing party’s on-camera rebuttal to the president’s annual prime-time address to the nation, filled with pomp, ceremony and standing ovations.