Born to a well known rugby league family of the Penrith area, Tim Sheens was educated at St Dominic's College in Penrith but spent his last two years of school at St Gregory's College, Campbelltown, where he was the school captain and first-grade rugby league captain in 1968.
Sheens had a lengthy playing stint with Penrith, playing 166 first grade games from 1970 to 1982 and scoring 11 tries. Starting his career as a backrower, he finished as a ball-playing prop. In 1974 he was named as the Panthers' Player of the Year, but had his jaw broken in the inaugural Amco Cup final against Western Division.
By 1982, Sheens had played a club record 258 games in all grades, but was unable to come to terms with the club for another season. Sheens was soon coaxed out of retirement though, playing one season with the Campbelltown City Kangaroos in 1983, captaining that club to the Group 6 Rugby League premiership that season.
In October 2006, in recognition of his contribution as a player, Sheens was named as one of the Penrith Panthers "Team of Legends".
Tim Sheens' brother, Bob, was also a first grade NSWRFL player for Eastern Suburbs.
Although his first ever game as first-grade coach was a 24–12 loss to St George, Tim Sheens has a track-record of reforming under-performing teams to premiership victory. He brought Penrith to their first finals series ever in 1985 and he coached the Canberra Raiders to their first premiership in 1989. In the post season he travelled with the Raiders to England for the 1989 World Club Challenge which was lost to Widnes.
Sheens won further premierships with Canberra in 1990 and 1994. However, his time with the North Queensland Cowboys (1997–2001) was less successful and, after board discussions, a period of stress-leave and while News Limited launched a take-over of the club, he resigned from North Queensland on 25 May 2001.
In 2002, Sheens accepted the coaching position with the Wests Tigers for the 2003 season, replacing Terry Lamb. The feat of the Wests Tigers winning the 2005 Grand Final against the Cowboys has been largely attributed to Sheens.
Sheens has coached four premiership winning teams, making him second only to Wayne Bennett among current coaches. Sheens was awarded the Dally M Coach of the Year in 1984, 1990 and 2005.
As NRL Premiers Wests traveled to England to play against Super League champions Bradford Bulls in the 2006 World Club Challenge. Sheens oversaw the Tigers' 30-10 loss.
In December 2007, Sheens' contract with the Tigers – due to expire at the end of the 2008 season – was extended to 2010.
On 3 May 2010 Sheens became the first coach in Australian rugby league history to reach 600 games. In 2011, Penrith Panthers offered Tim the job as head coach for the club. However, on 29 April 2011, Tim decided to stay coach for the Tigers and extended his coaching contract for until 2014. On 25 September 2012, after days of speculation about Sheen's future due to a poor recent season, the Tigers announced Sheens would not coach the team in the 2013 season, but offered him other roles at the club.
On 23 June 2015 Sheens become director of rugby league at the English rugby league club Salford Red Devils.
At the representative level, Sheens coached the 1991 ARL City Origin team to a 22–12 win over Country. In the same year, as coach of the NSW State of Origin team, he led the side to a 2–1 series loss to Queensland. In 1997 Sheens coached the NSW super league side to a 23 to 22 win over Queensland in a Tri series competition involving NSW Queensland and New Zealand.
Sheens returned to the NRL representative arena in 2006 when he succeeded Graham Murray as coach for City Origin, a post he retained in 2007 and 2008. In 2006, City lost to Country, 12 points to 10 but won in 2007, 12 points to 6. The 2008 match was a 22–22 draw, with City retaining the trophy.
In February 2009, Sheens was appointed coach of the Australian national rugby league team following the resignation of Ricky Stuart. Sheens coached the Kangaroos to their first win in his charge, defeating the Kiwis on 8 May 2009.
He coached the Kangaroos in their successful 2013 Rugby League World Cup campaign. The Aussies conceded just four tries in the entire tournament (all to England in their opening match). He gave Australia revenge against New Zealand in the final after losing to them in the 2008 Final.
Sheens resigned as the Kangaroos head coach on 3 October 2015 to take up a full-time position as director of English Super League club Salford Red Devils. In September 2016 it was announced that he would join Hull Kingston Rovers for season 2017 and beyond.
As of 4 May 2015