Val Demings is planning to challenge Marco Rubio for one of Florida’s Senate seats.

MIAMI — Representative Val B. Demings, Democrat of Florida, intends to run for the Senate next year, two people with knowledge of her plans and the party’s strategy on Senate races said Tuesday. Her entry into the race gives Democrats a high-profile challenger against Senator Marco Rubio, the incumbent Republican.

Ms. Demings is expected to formally announce her candidacy in the coming weeks, according to one of her advisers. Her plans were first reported by Politico.

Her impending campaign comes as Florida Democrats, battered from mounting electoral losses there since 2016 and by former President Donald J. Trump’s comfortable win in the state last year, jostle over how to best take on Mr. Rubio and Gov. Ron DeSantis, a Republican, who also faces re-election next year.

Ms. Demings, a former police chief who represents a district in Orlando, had been weighing whether to run for Senate or for governor. Mr. DeSantis is a top target for Democrats because if he wins re-election, he will be considered an early favorite for the Republican presidential nomination in the 2024 election. Early signals suggested Ms. Demings was leaning toward the governor race: When Representative Charlie Crist declared his Democratic candidacy against Mr. DeSantis this month, her team released a polished biographical web video on the same day.

But Mr. DeSantis is a formidable foe whose political committee raised nearly $14 million in April, an intimidating sum for his would-be challengers. Besides Mr. Crist, Democrats also expect Nikki Fried, the Florida agriculture commissioner, to run for governor. (She has teased an announcement for June 1.)

Ms. Demings ultimately favored a Senate run because she could continue the legislative work she has done in the House but make a bigger difference, said her adviser, who requested anonymity to discuss internal deliberations.

In the House, Ms. Demings made a name for herself as an impeachment manager during Mr. Trump’s first trial last year. She was also a contender to be selected as Joseph R. Biden Jr.’s vice-presidential choice last summer.

Ms. Demings could find herself running against familiar faces: Among the Democrats also considering Senate runs are two from the Orlando area, Representative Stephanie Murphy and former Representative Alan Grayson.

“It’s become clear to me that the only thing Marco Rubio cares about is Marco Rubio, so I think he needs to retire or be retired,” Ms. Murphy, who has been on a tour of the state, said in Tallahassee on Monday night, according to The Tallahassee Democrat newspaper.

In a statement, a spokesman for Mr. Rubio said Democrats “are tripping over themselves” to find a candidate. “While Democrats are flailing to find their next candidate to advance their radical agenda, Senator Rubio is focused on delivering wins for the people of Florida,” the statement said.