Five months ago, he told local reporters in St. Paul, Minnesota
, that he wanted to be a part of the police force in part because of the death of his nephew, who was shot and killed by a police officer during a traffic stop in 2016.
"It drives me to be upfront and center with a uniform on, and tell young people they have nothing to fear," he told CNN.
By being a part of the police force, Castile says he wants to educate the public about the roles and responsibilities of police and look for ways to improve police training.
"We can't blame the whole police force because of the actions of one guy. I know that people get killed every day, but by better training of those people, less of those mistakes will happen."
As a reservist, Castile says he will be involved in things like traffic control, event safety, and crime scene preparation.
"I will [also] be going to rec centers, and teaching the community police terminology they may not know the meaning of," Castile says.
The St. Paul Police announced Castile's appointment, as well as the appointment of 14 other Police Reserve Academy Graduates, on their Facebook page.
"We're so happy to have so many wonderful people willing to support our efforts to build connections with the community and keep Saint Paul safe," the department wrote
Castile received mixed responses after his decision to join the police force.
"A lot of people expect for my family to be angry and begrudged and we aren't. It's a negative thing and we believe that if we take that negative energy and turn it into something positive, we'll have more positive results. "
Philando Castile's killing in July 2016
was one of several police-involved shootings that year that rubbed salt in the wounded relationship between police officers and black communities. It was hallmarked by a brutal Facebook live video recorded by Castile's fiancee, Diamond Reynolds, in which she detailed the events of the shooting as Castile lay bleeding next to her in the car.
A year later, Jeronimo Yanez, the officer who fatally shot Castile, was found not guilty of second-degree manslaughter
Clarence Castile told CNN affiliate KARE
that he thinks about his nephew every day.
"Part of this is about him," he said.
He also told CNN that his new job comes with the blessing of the Castile family.
"My family supports me 100%," he says. "Philando's mom [his sister] gave me congratulations."
Castile hopes the opportunity will allow him to help repair the mistrust that often marks the relationship between police officers and the public, but he knows there is a lot of work to be done.
"It can't be a one-sided thing," Castile says. "I'm only one person, trying to help rebuild the relationship. I'm a reserve officer. The real cops, they're going to have to get to know the people in the community."
Castile said he believes the other side of the relationship also has a duty to help in erasing the prejudice and misunderstanding many have against police officers.
"Most people expect for the police to be the ones that de-escalate and escalate the situation, but in reality, us citizens tend to escalate things. We need to understand what we're doing and then work backwards. Learn how to de-escalate, to slow situations down ... so once we learn how to use these resources like law enforcement, I think a lot of people will be saved."
This article has been corrected to say that Clarence Castile was speaking to reporters in St. Paul, Minnesota.