Josiah Matthew Duggar was born on August 28, 1996, to Jim Bob Duggar and Michelle Ruark. He was the couple's eighth child, and they went on to have eleven more children after him.
Josiah was often said to be a playful child, and was often seen playing pranks on his family. He had a close bond with his younger sister, Joy-Anna, as a child and the two were often found playing together.
Like most children, Josiah was assigned chores growing up, which the family called "jurisdictions". In 2004, one of Josiah's jurisdictions was taking out the trash. In 2011, Josiah's jurisdictions including cleaning the bathrooms.
By 2001, Josiah's parents had implemented a buddy system, where each older child was paired with a younger child to take care of. Typical tasks for an older buddy included dressing, bathing, and feeding their younger buddies. It is likely that Josiah was a younger buddy in this system, at least for a short time. By 2009, the family had switched from individual buddies to buddy teams, with each team being led by one of the oldest four daughters. Josiah was not assigned to a buddy group.
In 2006 Josiah and his family moved into a new home in Tontitown, AR. The family made a point of doing much of the work on the house themselves, seeing it as a learning opportunity for their children. In this house, Josiah was given a dormitory-style room with his brothers. He briefly lived in the Cornish House in Little Rock, AR, after the birth of his youngest sister, Josie, as the family wanted to be closer to the NICU where she was being taken care of.
Thanks to his family's reality show, Josiah traveled much of the world as a child. Notable vacation locations include Disneyland, New York City, Niagara Falls, Scotland, Ireland, London, Israel, China, and Japan.
Josiah was homeschooled growing up. He took the test to get his GED in 2014, at seventeen years old. His family had a graduation party to celebrate this event.
Josiah was raised as an active participant in Bill Gothard's Institute for Basic Life Principles. In 2014, Josiah attended ALERT Academy, the institute's version of the ROTC. 
Josiah began taking piano lessons from Ruth Anita Anderson, who he and his siblings referred to as "Nana", as a young child. He also took violin lessons. As an adult, Josiah has been seen playing the cello, but it is unknown when he learned this instrument. 
See also: Josiah Duggar and Lauren Swanson Wedding
Josiah surprised Lauren Swanson by showing up during a girl's night out with some of his siblings and asking her to enter an official courtship, which she said yes to. The two publicly announced their courtship on January 23, 2018, on the Duggar family's website.
On March 5, 2018, Josiah announced on the Duggar family website that he and Lauren Swanson were engaged. He proposed on Lauren's family's property, in the same place where Lauren's parents got engaged.
Josiah married Lauren Swanson on June 30, 2018, at John Brown University's Cathedral of the Ozarks in Siloam Springs, AR. His best man was his brother Joseph, and his groomsmen were his brothers Jedidiah, Jeremiah, Jason, and James Duggar, his brother-in-law, Austin Forsyth, one of new future brothers-in-law, and a friend, with one of his new brothers-in-law as his ring bearer.
On November 8, 2019, Bella Milagro Duggar was born. She weighed 6 lb, 5 oz, and was 18.5 inches long.
Much of Josiah's chlidhood was spent on TV. On September 6, 2004, Discovery Health Network aired an hour-long special titled "14 Children and Pregnant Again!" This special introduced television viewers to the Duggar family, including eight-year-old Josiah. This special was followed by four more specials, "Raising 16 Children", "16 Children and Moving In", and "On the Road with 16 Children", which all aired in 2006, and "Duggars' Big Family Album", which aired on September 22, 2007.
On September 29, 2008, the show 17 Kids and Counting premiered on TLC. This show was a weekly half-hour reality show chronicling the lives of the Duggar family. Josiah was regularly featured on the show. Many of Josiah's adolescent milestones, including getting his driver's license and graduating high school, were featured on this show. Later renamed 18 and then 19 Kids and Counting for the births of Jordyn and Josie Duggar, this show aired for 10 seasons. On July 16, 2015, amidst scandals involving Josiah's oldest brother, Josh, TLC announced that they were canceling 19 Kids and Counting.
On December 13, 2015, the first installment of a three-part special titled Jill & Jessa: Counting On aired on TLC. These specials focused on the family moving on after the scandals of the previous summer. Although the specials were focused primarily on Josiah's sisters Jill and Jessa, who had both recently married and were starting families, Josiah and the rest of his adult and older teenage siblings were featured as well. This show was picked up as a regular weekly reality show shortly after, and was renamed Counting On for season 3 when Josiah's sister Jinger's courtship became a central focus of the show. Since then, it has focused more on all of the adult Duggar siblings. Josiah's courtship, engagement, and wedding were one of the central focuses of season eight, which aired from July 30, 2018, to November 27, 2018.
Josiah has gone on a number of mission trips in his life. His family regularly goes on a mission trip to Central America every December, and Josiah is usually a part of that trip.
He also sometimes accompanies his family members to disaster relief projects in the US, with one notable example being helping after a massive tornado hit Joplin, MO. 
Josiah currently has his private pilot license. This license was issued in September 28, 2016, and allows him to fly planes with single engine landing.
Commercial Driver's License
A 2016 episode of Counting On showed Josiah training to get his CDL, which would allow him to drive larger vehicles like semi-trucks and commercial buses. It is unknown if he ever received this license.
On April 6, 2015, Josiah entered a courtship with Marjorie Jackson. The two met when her mother taught Spanish classes to Josiah and his siblings. Although Marjorie says she fell for Josiah almost immediately, he did not begin to fall for her until the two went on a mission trip to El Salvador in December of 2014. This courtship was announced to the public on April 13, 2015. The courtship was scheduled to be featured on the show 19 Kids and Counting, but the show was cancelled before this could happen. On August 5, 2015, the couple announced that they had ended their courtship. According to a statement by Josiah on March 9, 2016, it was Marjorie who chose to end the courtship. Although it was speculated that this break-up was a direct result of the scandals regarding Josiah's oldest brother, Josh Duggar, this was never confirmed.
Josiah has been involved in the following weddings:
- groomsman: his brother Josh Duggar's wedding to Anna Keller (9/26/08)
- groomsman: his parents Jim Bob and Michelle Duggar's vow renewal ceremony
- groomsman: his sister Jessa Duggar's wedding to Ben Seewald (11/1/14)
- best man: his brother Joseph Duggar's wedding to Kendra Caldwell (9/8/17)
- "Who's the Most Romantic?." Counting On. TLC. Silver Spring. 15 Oct. 2019. Television.