Larkham made his test debut as a reserve against Wales in Sydney in 1996 when he replaced injured Ben Tune on the wing, and then joined the Wallabies on their undefeated tour of Europe.

In 1997, Larkham proved more than a capable replacement at fullback for the injured Matt Burke, with a two-try effort in the Wallabies final Test against Scotland at Murrayfield.

[2] Larkham's conversion from fullback to flyhalf is now hailed as a Rod Macqueen masterstroke that put the Wallabies on track to win the 1999 Rugby World Cup.

[citation needed] This was initially a controversial selection as his tactical kicking was regarded as too weak for the position; however, his ability to get the Australian back line going and to slide through gaps himself quickly ended the debate.

Simon Poidevin while commenting for Australian TV remarked during the third test against the All Blacks in 1998 that "anyone who thinks (Larkham) is a dud flyhalf needs their head read" (i.e. is wrong) and this was eventually accepted to be correct.

[citation needed] South Africa had got to the semi-final largely through the efforts of Jannie de Beer kicking five drop goals in their previous match.

The fact that Larkham had quite a badly injured knee through the match caused Steve Smith to remark incredulously while calling the game for English ITV "He can barely stand on that leg and yet he just thwacked it over."

On 18 February 2018, he received the GENLEC Player of the Day jacket for his great play and sportsmanship in the Clare Holland Cup charity match.

Larkham and newly appointed head coach Jake White made a formidable duo, as during the 2012 Super Rugby season, the Brumbies went from being the fourth best Australian franchise to the second best behind the Queensland Reds.

He guided Matt To'omua and Christian Lealiifano to world class fly-half options, which helped the Brumbies secure the top Australian conference position during the 2013 Super Rugby season, finishing second overall losing in the final to the Chiefs 27–22.

[7] That campaign saw a marked improvement in the team's performance, with the Australians winning the shortened Rugby Championship competition that year, going on to eliminate World Cup hosts England in pool play, and contesting the final against New Zealand (losing 34–17).

[8] Larkham remained with the national side until February 2019, when he was controversially sacked by Cheika after coming under intense pressure following a number of years of poor results.