The 32-year-old has battled back from an achilles problem that required two operations and has kept him out of the limelight since March 2000. His last game for the Newport first-team was against Swansea at Rodney Parade on 11 March, 2000.
Capped four times as a replacement for Wales, he made his Test debut in South Africa in 1998 and was a try scorer in the 1999 World Cup clash with Japan in his final appearance. He also toured Argentina with Wales in the summer of 1999, playing in two provincial matches, and scored two tries for a Wales XV in their 53-24 victory over the USA in Cardiff prior to the World Cup.
Over the years, he has scored 42 league tries for Ebbw Vale, Newport and Neath and his last league try came against Caerphilly in the 46-13 win in October, 1999.
'David has been striving to get back and has played a number of games with our Under 21s and United side. He came through Monday night's game against Leicester Extras and has earned his opportunity to return to the senior squad,' said Newport team manager Jim McCreedy.
'It's a chance for him to get back into the first-team set up. We are delighted to see him back and he is deserving of the highest praise for the way in which he has battled against adversity.
'Many people thought he would never be able to return to the professional tier of the game, but he has worked his socks off to get back into shape and can now play out the rest of the season in the hope of obtaining a contract for next winter either here at Newport or with another side.'
Llewellyn is included among the replacements along with James Richards, who returned to action with the United against Leicester having recovered from a neck injury. He is due to have another meeting with the specialists before the weekend and hopes to be able to return to first-team duty having missed the last two league games.
Newport are currently lying in third place in the Welsh Premiership table with four wins from seven games. Their 27-25 reverse at home against Neath in their last game ended a run of three successive victories.
For the record, Newport lead Caerphilly 8-4 in league matches and have won the last six matches, outscoring the Castlemen 38-11 in tries over those games. Caerphilly's last win in the series came in the 1998/99 season, when they beat Newport five times in the season.
Newport Rugby Percy Montgomery; Matt Mostyn, Jason Jones-Hughes, Jon Pritchard, Alex Cadwallader; Shane Howarth, Ofisa Tonu'u; Rod Snow, Paul Young, Chris Anthony, Simon Raiwalui (captain), Ian Gough, Steve Ojomoh, Jason Forster, Andy Powell.
Replacements: Adrian Garvey, James Richards/Dave Pattison, Matthew Veater, Rhys Jones, David Llewellyn, Jason Strange, Hal Luscombe/Nathan Brew.
Caerphilly: S Tuipulotu; J Murphy, R Boobyer, S Cox, G Lewis; J Thomas, A Chilten;L Manning, C Ferris (capt), D Sweet, N Rouse, D Davies, G Jones, A Williams, J El-Abd.
Replacements: L Richards, O Ashman, G Liddon, F Vunipola, S Grainger, PJones, M Workman.
Previous league meetings: Newport lead 9-4 overall, including 4-2 in wins at Caerphilly.
Last season: Newport 50 Caerphilly 22; Caerphilly 20 Newport 46.
This season: Newport 36 Caerphilly 10 (Premiership - October 29)