Pienaar returned in mid-October after spending six weeks on the sidelines with a knee injury and Martinez is delighted with his progression.
The 31-year-old midfielder has made nine appearances this season and he completed 88 per cent of his passes in the 4-0 thrashing of Stoke on Saturday.
Martinez is convinced the South Africa international has now recovered his fitness levels and expects him to go from strength to strength.
"He's such a special footballer and what he brings to us into the way we play is quite unique," he told the Liverpool Echo. "Stevie's experience is a valuable part of his squad and it's real bonus to have him back at his best.
"Not many players have his appreciation of space and close control, or the quality in one versus one situations when he opens the spaces and allows other players to come in.
"He has that composure and time on the ball, and slowly he's regaining his full fitness and he'll get back to his best."
