The 26-year-old was linked with a move to McDiarmid Park earlier this month but was a surprise starter, albeit as a right centre-back, in the Scottish Cup fourth-round victory over Cove Rangers last week – his first competitive appearance in green and white since, coincidentally, last season's Scottish Cup final defeat by the Saints at Hampden.
However, the Swede was omitted from the matchday squad to face Motherwell on Wednesday night and with the player himself stating that he didn’t feature in the long-term plans of Hibs boss Shaun Maloney, his Easter Road departure doesn’t come as a huge shock.
Saints boss Callum Davidson has already brought in four new faces but had earmarked Hallberg as the ideal recruit for his midfield from the start of the January transfer window.
The Scottish Premiership basement boys are on a wretched run of 12 games without a win, including a Scottish Cup exit at the hands of League Two side Kelty Hearts.
Hallberg signed for Hibs during Paul Heckingbottom’s tenure on a three-year deal and made 61 appearances, scoring three and registering five assists.
His versatility has seen him deployed in his natural central position as well as right-back, right-midfield, centre-back, defensive midfield, number ten, and as an auxiliary centre-forward on occasion.
A serious knee injury picked up in pre-season ruled him out of the first half of the campaign but he is now fit and will offer Saints something different in midfield as they look to turn around their form.