Rachel Reeves, the previous Labour pensions spokesperson, was promoted to shadow chief secretary to the Treasury in last week's reshuffle.
McClymont was formerly an opposition whip and is a member of the science and technology select committee.
He was also formerly a member of business, innovation and skills select committee.
Before entering parliament in May 2010, McClymont taught history at Oxford University where he completed his PhD.
Hargreaves Lansdown head of pensions research Tom McPhail said the new shadow pensions minister would have a challenging brief and a very short amount of time to prepare before next week's debate on the Pensions Bill.
McPhail added: "He has voted against auto-enrolment and against encouraging occupational pensions provision, so what exactly is he in favour of, and where does this leave the cross-party consensus on the auto-enrolment reforms?"