The striker had a trial with the club last week and scored in a reserve fixture against Lincoln City. It is Tai's second loan spell away from the club this season having previously spent half a season at local neighbours Kidderminster Harriers.
Darlington are chasing a League Two play off place and have called for Tai to offer competition for striking positions. He will be competing with other loan strikers Andy Cooke and Jermal Johnson for a starting place.
Tai has found it difficult to force his way into first team football at Walsall. He made his debut last season in the virtual reserve side that lost out to Sheffield Wednesday in the first round of the League Cup.