Rep. Charlie Dent, R-Pa., announced Tuesday he will leave Congress in the "coming weeks," earlier than expected.

Dent, 57, announced last year he will not seek re-election in November. The reason for the timing change was not clear.

"After discussions with my family and careful reflection, I have decided to leave Congress in the coming weeks," Dent said in a statement. "Serving the people of the 15th Congressional district has been a tremendous responsibility and the privilege of a lifetime, and I am honored by the trust that so many of my constituents placed in me to represent them in Washington."

Dent, a moderate Republican and occasional critic of President Donald Trump, has served in the House since 2005, representing a district between Harrisburg and Easton in east-central Pennsylvania. Under newly redrawn Pennsylvania congressional districts, Dent would have run in a revised 7th District, which has moved in Democrats' favor, according to nonpartisan election handicappers.

Dent's new district is considered a possible pickup opportunity for Democrats as they try to flip 23 seats to take a House majority. He is among multiple House Republicans from Pennsylvania who decided not to seek re-election.

In a statement, National Republican Congressional Committee Chairman Rep. Steve Stivers of Ohio said the group will "work tirelessly to keep this seat under Republican control." Pennsylvania Republican Party Chairman Val DiGiorgio said the party "will work vigorously to ensure the resources and effort are available to keep this seat red."

Pennsylvania's Democratic Gov. Tom Wolf will make a decision on whether to hold a special election to replace Dent once he receives the congressman's official resignation, Wolf's office said in a statement. Under state law, a special election can occur more than 60 days after the governor issues an order about filling the vacancy.

A special election would be for the unrevised 15th District.

House Speaker Paul Ryan got a "heads up" about Dent's decision to leave Congress, his spokeswoman AshLee Strong told CNBC. She did not say whether the speaker supports the move.

Dent showed a tendency to sometimes break with his party on key issues. He voted against a House Republican plan to repeal and replace the Affordable Care Act last year.

Dent has criticized Trump's comments about immigrants and the president's remarks about violence at a white supremacist rally in Charlottesville, Virginia, last year. He also introduced a version of a bill to protect special counsel Robert Mueller from possible attempts to remove him. Mueller is investigating Russian efforts to interfere in the 2016 election and whether Moscow coordinated with the Trump campaign.

Dent did vote with Republican leaders to approve the tax overhaul signed into law in December.

In December, he told CNN that Trump was one of the factors in his decision to retire.

— CNBC's Brian Schwartz contributed to this report.