Karran worked as a joiner. He stood for election in Middle in the 1981 Manx general election but was not elected. In 1985 he contested a by-election in Middle and was elected, becoming the youngest ever elected Member in the House of Keys. In the 1986 general election, Karran contested Onchan and was elected. He repeated his success in Onchan in general elections in 1986, 1991, 1996, 2001, 2006 and 2011. He has been very popular ever since, topping the Onchan polls at most elections. (In 2006 he received more votes than any other candidate for the Keys.)