She won the Women's Chinese Chess Championship in 2010 and 2014.[6] In July 2011 she won the Hangzhou Women Grandmaster Chess Tournament undefeated with a score of 6½/9 points, ahead of the then women's world champion Hou Yifan.[7] In October 2011 she took the second place at the Nalchik stage of the FIDE Women's Grand Prix 2011–12 with 7/11, ranked only after her compatriot Zhao Xue; her performance was enough to acquire her third and final norm required for the Grandmaster title.[8] However, one of the three norms was missing the signature of the arbiter, disqualifying her for consideration for the title.[9]
From June 18 to July 2, 2014, in the 5th stage of the FIDE Women's Grand Prix 2013–14 held in Lopota Resort, Georgia she finished jointly second with Elina Danielian and a 7/11 score. This marks her fourth GM norm. In the 6th stage of the FIDE Women's Grand Prix 2013–14 held in Sharjah, United Arab Emirates, from August 24 to September 7, 2014 she placed joint first with Hou Yifan with a score of 8½/11, winning the event thanks to a better tiebreak score.[9]
In November 2014, FIDE awarded her the GM title in the 4th quarter Presidential Board meeting in Sochi, Russia.[10] With six GM norms, including three norms from the Women's Grand Prix (1 from each series), she is now a fully fledged grandmaster, China's 31st grandmaster and the 31st woman to hold the title. Also in 2014, she tied for first with Lei Tingjie in the 4th China Women Masters Tournament in Wuxi.[11]
Ju earned the biggest win of her career in the fifth round of the Tata Steel Chess Tournament 2024, defeating then world number 6 Alireza Firouzja.[16] She also drew World Champion Ding Liren in the final round, and eventually finished the tournament in 10th with 4½/13 (+1-5=7), gaining 9.7 rating points.
Ju Wenjun has played for the Chinese national women's team since 2008. Her team has won the gold medal in the 42nd Chess Olympiad in 2016, Women's World Team Chess Championship in 2009 and 2011, Women's Asian Nations Chess Cup in 2012, 2014 and 2016, gold medal in the Olympiad at 2018, and 2010 Asian Games.
In 2013, she won the silver medal with team Shanghai in the Asian Cities Chess Championship in Dubai.