In the 1986 general election, Weller challenged incumbent Democratic Representative Ray A. Christensen in the 85th district.

Weller won a crowded Republican primary, and defeated fellow State Representative Frank Giglio in the general election.

[9] In 1995, Weller received an Environmental Protector Award from the Chicago Audubon Society for his political service.

[10] After a release of tritium from Exelon's Braidwood and Dresden Nuclear Power Plant Weller sent a letter to Exelon Corp expressing his concern and recommended that the Nuclear Regulatory Commission investigate the power plants in question.

[16] Weller supported free trade when serving in Congress and traveled throughout Latin America and the Caribbean to build better relationships with public sector and business leaders.

He supported the use of tax incentives to help redevelop brownfield formal industrial land, developing a proposal with Democrats, such as Chicago Mayor Richard M. Daley, to do so.

[20] Weller sponsored a bill to expand concurrent receipt for wounded military veterans, but it did not pass.

[21] Weller sponsored a bill to make the residential energy efficient property credit permanent, which never left committee.

[25] Weller and 11 other congressmen were subpoenaed to testify in the trial of Brent R. Wilkes, the contractor accused of bribing Cunningham.

[27] Weller was the only member of the House of Representatives to abstain in the vote for the proposed bailout of U.S. financial system (2008).

"[37] On September 7, 2007, the Chicago Tribune disclosed the results of their own investigation into his land deals, including discrepancies on declared prices and numbers of transactions, centered in the Playa Coco resort area.

[38] No inquiry was ever launched by the Democratically-controlled House,[39] but Weller announced that he would not seek reelection on September 21, 2007.