The service for Kirk, whom Trump credits with playing a pivotal role in his 2024 election victory, is expected to draw tens of thousands of mourners, including senior White House officials and young conservatives shaped by the 31-year-old firebrand.
The event will take place at 11am on Sunday (4am Monday AEST) at a football stadium, with a capacity of 63,400, in Glendale, Arizona, where Kirk lived with his family.
Tens of thousands of mourners are expected to attend, with Trump and Vance scheduled to speak alongside Kirk's widow Erika, with very tight security precautions expected.
Kirk's assassination on September 10 at a Utah college campus set off a fierce debate about violence, decency and free speech in an era of deep political division.
The shooting also has stirred fear among some Americans that Trump is trying to harness outrage over the killing as justification to suppress the voices of his critics and political opponents.
His death has provoked concerns over Trump and Vance's calls to punish people who condone or rejoice over Kirk's death. Critics say such speech is protected under the US Constitution's First Amendment.
Kirk was very close to Trump's government and his family. The activist founded the Turning Point USA organisation in 2012, which is now active at numerous schools and universities.
Trump has blamed the "radical left" for Kirk's death and threatened to go after liberal organisations and donors or others whom he feels are maligning or celebrating Kirk's death.
Through his platforms - including a successful podcast - Kirk reached an audience of millions, especially young people. Critics accused him of spreading racist, homophobic and sexist views.
Dozens of people, from journalists to teachers, already have lost their jobs as prominent conservative activists and administration officials target comments about Kirk that they deem offensive or celebratory.
The retaliation has in turn ignited a debate over the First Amendment as the Trump administration promises retribution against those who air what are seen as disparaging remarks in the wake of Kirk's death.
ABC pulled Jimmy Kimmel's late-night show off the air indefinitely following backlash from affiliated broadcasters and the Trump-appointed head of the Federal Communications Commission over the comedian's remarks about Kirk.
The State Department also warned it would revoke the visas of any foreigners who celebrated Kirk's assassination.
A 22-year-old Utah man, Tyler Robinson, has been charged with killing Kirk and faces the death penalty if convicted of the most serious charges.
Authorities have not revealed a clear motive in the shooting, but prosecutors say Robinson wrote in a text to his partner following the shooting that he "had enough" of Kirk's hatred.
with AP
