He moved with his family as a child; after spells living in London and Zambia, he attended the Catholic ex-junior seminary St Patrick's Classical School in Navan, where his schoolmates included Hector Ó hEochagáin and Dylan Moran.
[6] He has also appeared on Michael McIntyre's Comedy Roadshow, The Lee Mack Show, Dave's One Night Stand, QI, and joined Eddie Izzard and Ross Noble at Laughs in the Park.
In "Going to America", the final episode of the clerical sitcom Father Ted, Tiernan plays a young priest.
In the 1999 Channel 4 sitcom Small Potatoes, Tiernan took the lead role of Ed Blewitt, an underachiever who works in an east London video rental shop.
[9] An appearance on The Late Late Show in 2008 led to complaints about Tiernan's jokes involving a methadone user, Eastern European immigrant accents, buying a motorbike from an injured biker, and a film idea about "gay Traveller spacemen" seeking a cure for gayness, eight of which were upheld by the Broadcasting Complaints Commission.
Some of his previous routines which went largely without remark included a comic reference to disproportionate American reaction to 9/11 and the indifferent Israeli attitude to foreign criticism of their occupations of surrounding land.
[10][11][12] In September 2009, while being interviewed by Olaf Tyaransen for Hot Press magazine at a pre-performance Q&A session at Electric Picnic in County Laois, Tiernan was asked by an audience member if he had ever been accused of antisemitism.
"[14][15] He later suggested in several interviews that his points were intended as a commentary on how somebody's words can easily be taken out of context when a small segment of a dialogue is quoted.
The response of the audience was criticised as "disappointing" by Fine Gael's Alan Shatter, who also said, "I would regard it as particularly sad that people found that sort of outburst in any way amusing.
[16] He said that the comments were part of an attempt to explain his belief that comedians have a duty to be "irresponsible and reckless", to allow "whatever lunacy is within you to come out", and that they should never be taken out of context.
[19]Hot Press editor Niall Stokes defended Tiernan: "To interpret it as anti-Semitism is wrongheaded in the extreme.
[14] He said the last question asked from the floor about a "dogged charge of anti-Semitism" led to the comments, and part of Tiernan's response recounted criticism of his routine by a Jewish couple after a show in New York City.