Simon Charles Jonathan Danielli clearly enjoys Rugby World Cups. In the 2003 tournament in Australia he claimed three tries and in the 2011 competition in New Zealand he notched a crucial brace in the opening victory over Romania.

Simon missed the 2007 Rugby World Cup. It would have been his second RWC, but he returned to Scotland duty as a replacement in the RBS Six Nations Championship match against Wales at the Millennium Stadium in February 2008, his first international since the 2005 match against Ireland. That international return was bracketed by two Scotland A games the same month – victories against the Italians (at Mogliano) and Ireland (at McDiarmid Park, Perth). He was recalled for his first start for more than three years when Scotland visited Italy for the final match of the RBS Six Nations Championship, but his appearance was cut short by injury early in the contest. He recovered in time to play in the first Test on the two-match tour to Argentina. Because of injury he could not be considered for the 2008 autumn Tests that year, but he was back in the Scotland XV for the Six Nations Championship match against France in Paris in February 2009. Two weeks later he scored his sixth international try when Scotland beat Italy 26-6 at Murrayfield. A brace in the last ten minutes of Scotland's opening RWC 2011 fixture against Romania brought the tally to eight.

Simon made a try-scoring start to his Scotland career when he crossed in the comprehensive win against Italy in the 2003 RWC Countdown Test. In his first start of the 2003 Rugby World Cup, against the USA, he powered Scotland to victory with two tries – bringing his tally to four in as many caps. That match followed on from Scotland's first game in the tournament against Japan when he came on as a replacement and scored with his first touch of the ball. He also crossed the try-line in his Murrayfield Six Nations debut against England in February 2004, but he had to wait five years for his next international try (his sixth). However, injury curtailed his participation in the 2004 summer tour to Australia, limiting him to only outings against New South Wales Country and New South Wales Waratahs.

He was in scoring mood also for Scotland A in the Barclays Churchill Cup in Canada in June 2006, with a try in each of the wins against England Saxons and Canada. He added to that tally in February 2007 with a try in the A international victory against Italy at McDiarmid Park, Perth. Later that year he played for Scotland A in two of the three Churchill Cup matches in England. Simon played for Scotland A against Ireland A in February 2010.

While at Cheltenham College, Simon played for English Schools in season 1997-1998, scoring a try in the Hughenden international against Scottish Schools. He then had representative rugby England under-21 and England Students before opting to pursue his birth qualification with Scotland. He played in three University matches (1998-2000) and graduated from Oxford in philosophy and theology. Simon, who played full back at Cheltenham College, cites his best moment in club rugby as a try he scored for Bath against Leeds Tykes in 2001-2002. A former member of the Scottish Exiles squad, he joined Bath from rivals Bristol Shoguns in 2001 and moved to The Borders in three years later. He joined Ulster in summer 2007.