[1] Marshall began his rugby union career with Southland and was then asked to join Christchurch by Canterbury coach Vance Stewart.

His New Zealand contract ran out after the 2005 Lions tour,[3] and he signed to play the 2005–06 season for Leeds Tykes in the English Premiership.

[9] Throughout the 2009–10 season, whilst continuing to play for Saracens, Marshall was a pundit and commentator on BBC Wales rugby programme Scrum V.[10] At the end of that season, he announced the end of his playing career with a view to moving back to New Zealand to focus on his broadcasting career there.

[11] In April 2013, Marshall made an unexpected comeback, taking the field for club side Wakatipu, at the age of 39.

[13] In the 2005 Queen's Birthday Honours, Marshall was appointed a Member of the New Zealand Order of Merit, for services to rugby.