McClaren said "Stuart had done very well to come through and win a regular place in the first team this season. He has shown a first class attitute in bouncing back from one or two injury set-backs and is very much part of my long-term plans."
Parnaby has been with Boro since he was eleven has has represented England at every level up to U-21 along his way.
The extension to Parnaby's contract comes a day after Boro revealed that they would make a bid to sign Cameroon international Geremi, on a permanent basis.
It would appear that the management team are now looking to prepare for next season. With Boro now on 38 points and in eleventh place it would be very unlikely that the team lost their Premiership status.