[7] Russell was selected to play for Ayr after the IRB Championship tournament, helping them win the league and cup double in the 2012–13 season of the Scottish Premiership.

With Glasgow's top players away on international duty for the 2013 Six Nations Championship, Russell was named on the bench to face Zebre on 10 February 2013 as part of the 2012–13 Pro12 season, coming onto the field and making his professional debut at the 56th minute of the game.

In the final match of the regular season, he scored 22 points (including two tries) in a bonus-point victory over Ulster which was needed to secure a home play-off.

[13] On 29 November 2017, it was announced that Russell would leave Glasgow Warriors at the end of the 2017–18 season to play for French club Racing 92, where he was to replace All Black Dan Carter who was moving to Japan.

[16] Russell sustained a groin injury during Bath's Investec Champions Cup defeat to Exeter Chiefs, taking him out of action for five weeks.

[17] He returned for the final two rounds of the regular season, playing a crucial role in helping Bath reach the playoffs for the first time in four years.

[20] Russell earned his first call-up to the senior national team during Scotland's summer 2014 tour of North America, where he started in the matches against the United States and Canada.

In 2014, Russell had what Scottish sportswriter Andy Newport called "a meteoric rise [that] saw the former Stirling County youngster blast his way into the national team in the space of six months.

In 2023 Russell was selected as one of two specialist stand offs, the other being Ben Healy, in Scotland's 33 player squad for the 2023 Rugby World Cup in France.

Following an instrumental man-of-the-match performance for Scotland against Australia in Sydney, Russell was called up as a replacement to the 2017 British & Irish Lions tour to New Zealand.

[32] He made a brief mid-week appearance during the 31-31 draw with Super Rugby champions Hurricanes[33] as replacement for Dan Biggar who had sustained a head injury, becoming Lion number #835.

[37][38] Russell's performance was widely praised, with former England scrum half Matt Dawson stating, “if he was an All Black, you’d be saying he’s the next Dan Carter, he’s that good”.

Russell has been nicknamed 'Russell the Muscle' due to having a somewhat slender build for a modern-day rugby player, and has also been given the moniker 'White Chocolate' by teammate Simon Zebo.