Mercer grew up in Northowram, near Halifax, but moved to Glasgow aged eight. He is the son of former New Zealand rugby league international Gary Mercer.
At 16 he was given a scholarship to attend Merchiston School in Edinburgh but he represented England at underage level.
A member of the Bath Rugby Academy, he made his debut in a 58-5 victory against Newcastle in September 2016, and has gone on to establish himself as a regular in the first team squad this season.
Mercer captained England U20's to the 2017 Six Nations title, winning the Grand Slam in the process and narrowly lost out to New Zealand in the U20 World Championship final that summer.
A strong ball carrier and a formidable force in defence, Zach signed a senior contract extension, which will see the Academy player promoted to the senior squad and commit his future to the Club until the end of the 2018/19 season.
Mercer was nominated for the (2016-17) RPA Young Player of the Year, as voted for by Aviva Premiership players based on performances in domestic rugby this season.
He continued to put in impressive performances with Bath and earned a call-up - as an apprentice - to the England squad for the November internationals.
The call-up was followed by an inclusion as one of 8 uncapped players in Eddie Jones' 35-man squad for the 2018 Six Nations opener against Italy.
On 27 May 2018, Mercer started for England at number 8 in a non-test match against the Barbarians, scoring a first-half try on his England debut.
Bath Rugby confirmed that Mercer agreed a two-year contract extension, which will keep him at the Club until the end of the 2020/21 season.
As of the 2018/2019 Champions Cup, Mercer has had 11 European Cups appearances scoring 4 tries and 20 points.
Mercer earned another England call up in November 2018
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