[6] Tennakoon next contested the parliamentary by-election for the seat of Kandy, held on 23 October 1954, representing the United National Party.
[8] On 20 April 1956, Tennakoon was elected as the Deputy Speaker of Parliament, a position he retained until 16 September 1958, when he was replaced by the member for Gampola, Richard Stanley Pelpola.
[9] He contested the newly created seat of Senkadagala at the 4th parliamentary election held on 19 March 1960, where he lost to Noel Wimalasena, of the United National Party by 1,157 votes.
[10] He re-contested the seat at the 6th parliamentary election, for the Sri Lanka Freedom Party, losing again to Wimalasena, this time by 3,370 votes.
He won the seat by 2,617 votes, defeating the sitting member, Mahahitana Arachchige Daniel, from the United National Party.