Toomey picked Tax Day for his announcement and stepped down as the chief of the conservative Club for Growth PAC this morning.
"Pennsylvanians deserve a voice in the U.S. Senate that will honor our values and fight for limited government, individual freedom and fiscal responsibility. I will be that voice," Toomey said.
"You see what I see a nation headed in the wrong direction," Toomey said in an online statement on his Web site. "The Washington politicians who helped get us into this mess are now making things worse."
In the video, Toomey said that he looks forward to an honest and fair debate but said that Specter was already running negative T.V. ads against him.
The Specter campaign, anticipating Toomey's announcement, began running a campaign ad in early April, the Pittsburgh Post-Gazette reported, which hits the former banker for his Wall Street career a decade ago.
According to the Associated Press, it was speculated that Toomey was eyeing a 2010 gubernatorial run, but switched his sights on the Senate after Specter was one of three Republicans who voted for the $787 billion economic stimulus bill.
Specter, who is running for his sixth consecutive term in the Senate, could not be reached for comment when contacted by cbsnews.com.
UPDATE: "Without Senator Specter's seat in the Senate, which Mr. Toomey would certainly lose, there would no longer be 41 Republican Senators to filibuster and stop the Democrats from passing Card Check, raising taxes, and implementing President Obama's massive spending plans," Specter's campaign manager Christopher Nicholas said in a statement to reporters.
"When Mr. Toomey today threatens a conservative 3rd party candidate to take 15 percent of the general election vote and defeat Senator Specter, he is the Democrats' best friend by giving them 60 seats in the U.S. Senate," Nicholas added.
In 2004, Toomey surprisingly ran a close race with Specter, loosing by only 17,000 of the 1 million votes cast.