Wallace burst on to the scene at the beginning of the 2001/02 season putting in a number of top class performances from fullback or out-half for Ulster.

He would return in time though to help his club, Ballymena, win the AIB All Ireland League Title, defeating Clontarf in the final at Lansdowne Road.

He began the 2003/04 season in the Number 10 shirt for Ulster due to David Humphreys absence because of the impending Rugby World Cup in Australia.

After fellow Ulster player Jonny Bell was ruled out of the tournament with an achilles tendon injury the uncapped Wallace was called up to the Ireland Squad.

Having been left out of the squad for the opening Heineken Cup game away to the Newport Gwent Dragons he was drafted into the 22 for the visit of French giants Stade Français to Ravenhill after an injury to Australian international centre Ryan Constable.

This secured the talented Wallace the Ulster Number 15 shirt for the next series of games including the 27–21 defeat of Edinburgh to lift the Celtic Cup, Ulster's first piece of silverware since the famous 1999 European Cup triumph, and the 33–0 thumping of Leicester Tigers at Ravenhill in January 2004, in the return leg of the Tigers' fixture though he had a torrid time playing at full-back and was relegated to the bench for the majority of the remainder of the season.

The 2004/05 season started well for Wallace; playing from out-half he hit the winning drop goal in the 17–16 defeat of Edinburgh at Murrayfield but after this the Ulster team and he both suffered a massive dip in form.

He made a number of appearances off the bench in this period but having come on for David Humphreys in the away Heineken Cup defeat to Gloucester he damaged knee ligaments that would see him ruled out until the new year.

The Ireland A team had a one-off fixture with France A at Donnybrook, Dublin with Wallace, playing out-half and kicking 12 points in the 15–9 triumph, putting in an accomplished display.

Injury to Humphreys towards the end of the season gave Wallace two further starts in Celtic League games against Cardiff Blues and Llanelli Scarlets.

He was selected by Ireland to tour Japan over the summer where he would have won his first full cap but his injury jinx struck again and a broken hand ruled him out.

He would continue to play for Ballymena before being once again drafted into the Ulster 22 for the Heineken Cup fixture away to Treviso where he came off the bench to score a try in the 43–26 bonus point win.

He retained his place in the starting line-up for the following week's trip to Stradey Park to face the Llanelli Scarlets and put in another solid performance in the no.12 shirt in the 12–12 draw.

He began the 2006/07 season partnering Paul Steinmetz in the centre and as since kept his place even keeping Ireland star Andrew Trimble on the wing.

Following that display, Wallace secured himself a place in the 6 Nations squad and won one cap during the campaign, coming off the bench in the historic 43–13 defeat of England at Croke Park.

Wallace was named in the Ireland Squad for the 2007 tour to Argentina and played in the first test, a 22–20 defeat to a last minute Felipe Contepomi drop goal.

Having previously been named on the bench for the test against New Zealand in Wellington the withdrawal of Leinster's Luke Fitzgerald gave Wallace a start in number 12 jersey.