WASHINGTON — Steady in her sneakers and grasping the helpful hand of a colleague, Rep. Gabrielle Giffords walked onto the House floor as colleagues approved her border security bill on the day she retired from elected office.

Giffords made her way down the center aisle that divides Democrats from Republicans, a distinction the Arizona congresswoman had tried to blur with her moderate politics and good nature. Colleagues quickly enveloped her slight frame, offering an outstretched hand — or, more often, a kiss on the cheek. In ovation, lawmakers stood.

Friends have said the three-term Democrat has never been one to tackle goals halfway. It was fitting, then, that she closed out her career on Wednesday with a legislative victory. The House unanimously passed the border security bill she had authored.

House Minority Leader Nancy Pelosi called Giffords “the brightest star that Congress has ever seen.”

“She has brought the word dignity to new heights by her courage,” Pelosi said. “Congresswoman Giffords’ message of bipartisanship and civility is one that all in Washington and in the nation should honor and emulate.”

The congresswoman was shot in the head a year ago after a gunman opened fire at a public event Giffords hosted for constituents outside a Tucson grocery store. Six people died and 12 others were wounded in a rampage that unsettled lawmakers and brought pleas for civility during an era of heated partisan politics.

Her last day in Congress was bittersweet, as emotional colleagues said farewell to the well-liked 41-year-old, who announced on Sunday that she would step down to focus on her recovery.

Rep. Eric Cantor, R-Va., the majority leader, said that “while Gabby may be leaving Washington today, I know this won’t be the last we see of her.”

Giffords’ mother, Gloria, watched from the House gallery along with the congresswoman’s husband, retired astronaut Mark Kelly. Her father watched from Tucson. The chamber was mostly full, and staff members ringed the back rows.

At one point, Rep. Steny Hoyer, D-Md., who called Giffords “an extraordinary daughter of this House,” said to her, “We have missed you.”

Giffords, who had turned backward in the chair to see her colleague, replied: “And I miss you.”

The legislation approved Wednesday would impose tougher penalties on those who use ultralight aircraft to smuggle narcotics. Officials believe the planes are carrying drugs into the United States across the southern border with Mexico with increased frequency. The bill, introduced this week with Rep. Jeff Flake, R-Ariz., closes a loophole that imposed lesser penalties on smugglers who use ultralights than autos or planes.

It passed unanimously 408-0, with Giffords casting her final vote.

Quick approval offered a gesture of goodwill from Giffords’ colleagues. A similar bill from Giffords had drawn bipartisan support in the last session of Congress, but died in the Senate where colleagues have pledged to give this one speedy treatment.

Giffords submitted her resignation, effective at the close of business Wednesday.

One of her best friends in Congress, Rep. Debbie Wasserman Schultz, D-Fla., read the letter on the floor through a tearful farewell, with Giffords at her side and surrounded by other Arizona lawmakers.

“As I have worked to regain my speech, thank you for having faith in my ability to be your voice,” Giffords wrote to her colleagues and constituents. “I have given all of myself to being able to walk back onto the House floor this year to represent Arizona’s 8th Congressional District. However, today I know that now is not the time.”

“I will recover and will return,” she concluded.

With that, Giffords climbed the steps of the House rostrum to deliver the letter to House Speaker John A. Boehner, R-Ohio, who embraced his colleague and wiped tears from his eyes.