The memorial service for Charlie Kirk on Sunday began with somber remembrances and anecdotes from friends before turning more explicitly to politics and vows to crush enemies of Mr. Kirk’s conservative movement.

Tens of thousands of mourners packed a football stadium near Phoenix — and spilled into an overflow arena nearby — for the event, during which President Trump and many members of his administration eulogized Mr. Kirk. Some vowed that his death would only strengthen his efforts to bring young people to the political right.

The service took place nearly two weeks after Mr. Kirk, 31, was assassinated while holding an event on a college campus in Utah. A 22-year-old man who prosecutors said had decried Mr. Kirk’s “hatred” has been charged in his death.

Many speakers invoked Christianity and described Charlie Kirk as a martyr.

The memorial service featured several religious figures and focused heavily on faith in paying tribute to Mr. Kirk, who frequently spoke of his evangelical Christianity.

Those mourning Mr. Kirk said his death was also an opportunity to spread his Christian faith. It also was a clear indication of the melding of religion and politics under Mr. Trump’s administration.

Vice President JD Vance said that all of Mr. Kirk’s acts had followed from his faith.

Mr. Vance and President Trump were among several speakers who called Mr. Kirk a martyr and said they were convinced that his movement would carry on even stronger after his death.

Stephen Miller, a White House deputy chief of staff and close adviser to Mr. Trump, said the service was both about mourning Mr. Kirk and “finishing his mission and achieving victory in his name.”

He railed against those who he said opposed Mr. Kirk and what he stood for. “They cannot imagine what they have awakened,” he said. “They cannot conceive of the army that they have arisen in all of us.” The assassination, he said, had made Mr. Kirk “immortal.”

Top Trump officials and conservative celebrities attended.

Among the tens of thousands of mourners inside the State Farm Stadium in Glendale, Ariz., were dozens of well-known conservative figures including at least 20 members of the Trump administration, many of whom were given speaking slots.

In addition to Mr. Trump and Mr. Vance, government officials at the service included Marco Rubio, the secretary of state; Pete Hegseth, the secretary of defense; Robert F. Kennedy Jr., who leads the Health and Human Services Department; and Kash Patel, the F.B.I. director, who has led the investigation into Mr. Kirk’s death.

Several current and former Republican lawmakers were also there, including the House speaker, Mike Johnson, Senator Ted Cruz of Texas and Matt Gaetz, the former Florida congressman.

Elon Musk was shown chatting briefly with Mr. Trump in a box at the stadium, as was Dana White, who leads the mixed martial arts organization Ultimate Fighting Championship. Also in attendance was Kyle Rittenhouse, who was embraced by conservatives after being acquitted of all charges that he had faced for killing two people and wounding a third during unrest over a police shooting in Kenosha, Wis.

Tucker Carlson, the former Fox News anchor, briefly spoke from the stage, and several other media figures, including Stephen K. Bannon, who hosts a podcast and has long advised Mr. Trump, were also seen there.

Erika Kirk described viewing her husband’s body and forgave his killer.

Erika Kirk, Mr. Kirk’s widow, publicly forgave the man who killed her husband, saying, “I forgive him because it is what Christ did.”

“The answer to hate is not hate,” she added, with many in attendance standing and cheering.

She had traveled to a Utah hospital shortly after the killing to view her husband’s body, and said that she had felt “shock,” “horror” and “a level of heartache that I didn’t even know existed.”

But, she added: “Even in death, I could see the man that I love.”

Ms. Kirk told The New York Times in an interview that she had learned of his death when Mr. Kirk’s longtime assistant called her and screamed “He’s been shot!” over the phone. She learned that he was dead while she was in the air, flying from Arizona to Utah.

On Sunday, she said she had kept a small secret from her husband — that he had one gray hair on the side of his head — and noticed it even when she viewed his dead body. She had never told him about it, she said, but indicated that she believed he was listening: “Now, he knows,” she said.

She closed her speech by looking up and saying, “I love you, Charlie baby, and I will make you proud.”

As she walked off the stage, she paused and looked around at the cheering crowd, appearing overwhelmed and burying her face in a handkerchief.

President Trump mixed tributes with a political rally speech.

Recounting Mr. Kirk’s life story — from community college dropout to a leading voice for the young conservative movement — Mr. Trump declared Mr. Kirk the “greatest evangelist for American liberty.”

The final speaker at the service, Mr. Trump said he had learned about Mr. Kirk’s shooting while holding an important meeting in the Oval Office, and had swiftly kicked everyone out.

“It was like a surreal experience,” he said.

Mr. Kirk said many things that provoked a backlash, but Mr. Trump said that Mr. Kirk had valued debate and “did not hate his opponents.” And that, Mr. Trump said, is where he and Mr. Kirk differed.

“I hate my opponent,” Mr. Trump said, standing behind protective glass on the stage. “And I don’t want the best for them!" He then addressed Ms. Kirk directly, smiling as he apologized for disagreeing with her husband.

Since Mr. Kirk’s death, Mr. Trump has increasingly tried to crack down on his political opponents and media companies that offer critical coverage.

And while Ms. Kirk forgave her husband’s killer, Mr. Trump described the man charged in the shooting as a “radicalized, cold-blooded monster.”

Mr. Trump often pivoted to what resembled more of a campaign speech. He spent several minutes talking about his administration’s efforts to reduce autism rates and his decision to deploy the National Guard and federal agents to Washington.

In all, the service lasted more than five hours. Many people had arrived to the stadium hours before the event, which was unticketed and first come first served.

At the close of the service, Mr. Trump called Ms. Kirk to return onto the stage and hugged her. They stood side by side as “America the Beautiful” played.

Elizabeth Dias, Jack Healy and Anushka Patil contributed reporting.