[9] DeWeese's ascent through the echelons of House Democratic leadership began when he was elected by his colleagues as Majority Whip in 1988.

With the election of fellow Democrat Ed Rendell as Governor of Pennsylvania in 2003, DeWeese was able to wield more influence than otherwise would have been expected from a Minority legislator.

Days before the General Assembly convened on January 2, 2007, Rep. Thomas Caltagirone of Berks County announced he would not support DeWeese as speaker but would remain a Democrat.

After criticism from the media and activist groups, DeWeese joined his colleagues in a near unanimous repeal of the pay raise.

Republicans and a small number of fellow Democrats, including Governor Ed Rendell, criticized DeWeese's move; but he stood by his decision, explaining that those who opposed the pay-raise legislation knew the realignment would be a consequence.

[15][16] In 2006, the Democratic party won a 102–101 majority in the House, giving DeWeese a second chance at the speaker's gavel.

Among them were Rep. Rosita Youngblood of Philadelphia, whom DeWeese accused of being "owned lock, stock and barrel" by Perzel Incorporated.

[12] DeWeese initially attempted to block Pennsylvania Attorney General Tom Corbett's investigation into whether the House Democratic caucus made illegal payments to staffers, with motions to quash subpoenas and exclude evidence seized.

[24] Evidence also showed that DeWeese and his top aides directed a state-paid consultant to perform political work.

His aides allegedly balanced his checkbook, paid bills, picked up dry cleaning, bought condoms, and arranged dinner dates from a list of women.

[32] Despite this reduced role in the Democratic caucus, the Pennsylvania Report expected DeWeese to "find some way to exert his influence and thus continue to be a power player and force behind-the-scenes in the PA House" and cautioned against anyone counting him out.

[3] After the verdict was delivered, DeWeese maintained the charges were politically motivated, and vowed to remain in the House until he was sentenced, at which time he said he would resign.

[5] DeWeese was the only Democrat to file for election to his House seat, and a Commonwealth Court judge ruled that his name could remain on the April 2012 primary ballot.

[41] Corbett, the former assistant General Counsel of Waste Management, opposes an extraction tax[42] on Marcellus Shale drilling while DeWeese favors it.

[6] In January 2012, DeWeese lambasted Corbett[46] for spending tens of millions of state dollars pursuing political enemies but ignoring the child abuse allegations against Jerry Sandusky; Corbett had received $201,783.64 in campaign contributions from past and present board members of Sandusky's charity, according to media reports.

DeWeese is well known for his idiosyncratic style of speaking and writing, which incorporates an extensive vocabulary, anachronistic usages, and attenuated metaphors.

When a man comes to my Capitol Hill enclave and stands beneath that impressive chandelier of gold, looks me in the eye with a gimlet gaze, shakes my hand with a sturdy grip and gives me his word, to me it's axiomatic that the gentleman is telling the truth.