Mackenroth was pre-med at the University of California, Berkeley for the first two years, following in the footsteps of his mom who was a nurse at Seattle's Harborview Medical Center, but later graduated with a double degree in Fine Arts and Sociology.
In 1991, Mackenroth moved to New York City to study Fashion Design at Parsons School of Design. After Parsons, Jack opened a menswear store on Bleecker Street in New York City's West Village called "Jack". In 1997, Mackenroth went to work for Tommy Hilfiger and then designed for Levis Slates brand. From 2003-2007, he was the Design Director at Weatherproof Active Wear.
On October 15, 2008, Mackenroth unveiled a custom-designed wedding gown crafted entirely of condoms as a visual reminder of the importance of safer sex and correct, consistent condom use for San Francisco's Project Inform.
As a fitness and fashion model through the 1990s, Mackenroth appeared in numerous magazines such as Paper, DNR, Men's Fitness, Men's Journal, Men's Health, Genre, Blue (Australia) and L'Uomo Vogue . After Project Runway, he graced the covers of many magazines including reFresh, POZ, HIVplus, and Gloss. His fashion illustrations have also been featured in Nylon, Elle, and in ad campaigns for Tommy Hilfiger and Sushi Clothing.
In 2008, Mackenroth also had a cameo appearance in the Sex and the City movie as "Hot Guy #17."
Mackenroth was a competitive swimmer in elementary and high school and continued competing after college at the Masters level. Jack has earned three All-American titles and in the summer of 2006, he set a national record for the breaststroke leg of the 4 x 50 meter relay at the Masters World Championships in Stanford, California.
Mackenroth first competed in the Gay Games in 1990 in Vancouver, British Columbia, without a team but won a bronze medal in the 50-meter breaststroke. He has won at least one gold medal in every one of the international competitions since.
His mother watched his relay team set the national record at the 2006 Gay Games.
He competed in the 2009 Outgames, held in Copenhagen, Denmark, and the 2010 Gay Games in Cologne, Germany, where he earned seven medals.
Mackenroth was solidly in the middle of the competition from the very start and never appeared in the "bottom three." The third challenge, however, allowed him to showcase his talent in developing menswear. The challenge was to create a three-piece menswear outfit for guest judge Tiki Barber. Mackenroth won the challenge and his winning design was then worn by Barber during an appearance on The Today Show.
At the fifth challenge, Mackenroth decided to withdraw after a contagious staph infection. After leaving the show, Mackenroth spent five days in the hospital recovering from the infection where he received an IV antibiotic twice daily.
Mackenroth has been very open about his positive HIV status. Since his diagnosis on August 18, 1990, he has tried to combat the stigma of HIV by living honestly and being a role model through professional and athletic achievements.
"I am most proud of the fact that I was open about my positive HIV status on the show and exemplified that a person can manage HIV and live a successful life," Mackenroth says. "Every time a person with HIV is open about his or her status it helps everyone who is living with the disease.... I am a living testament to what you can accomplish by letting go of shame and being your own advocate." After his departure from the show, Mackenroth received many letters and e-mails thanking him for his openness and honesty and for being a great role model.
In 2008, Mackenroth partnered with Merck & Co., Inc. to launch a national HIV and AIDS education campaign called Living Positive By Design. Living Positive By Design events have been held in Miami/Fort Lauderdale, Florida at the 2008 United States Conference on AIDS (USCA), Atlanta, Georgia and in New York City at the Gay Men's Health Crisis (GMHC) Fashion Forward 2008 fundraiser.
Mackenroth is also the creator of the anti-stigma campaign HIV Equal. He is credited with coining the phrase "HIV equal" as opposed to "HIV-negative" or "HIV-positive". The hope being that people will finally stop using the term in a derogatory manner and stop discriminating against people with HIV. He has also served as the media strategist at Housing Works - a non-profit in New York, which fights the duel crisis of homelessness and HIV/Aids where he created the Prep Heroes Campaign prepheroes.org. He was a spokesman for the Merck Pharmaceuticals HIV Education Campaign, "Living Positive by Design" for four years.
He is currently serving as the Senior Communications Officer at MSMGF (The Global Forum on MSM and HIV).
In January 2016, he was named Wet Platinum Man of the Year for 2015.
He has over a million followers on social media platforms. Most recently he created the "HIV Shower Selfie Challenge" media campaign which went viral and achieved over 26 million impressions in one week using the hashtag #weareallclean. The campaign was translated into eight languages and covered in over one hundred media outlets.