The new-look Saddlers were worthy winners over a Barnsley side which struggled to get into the game.
Following a goalless first half when Barnsley only survived following a man of the match performance from the former Walsall player Matt Carbon, the Saddlers took control to complete a comfortable win.
Walsall's decision to go into the game without a recognised striker, however, held them back in the first half despite mounting several promising attacks.
Barnsley were surprisingly off-colour in attack for a team beaten only twice in their previous 18 away games. They appeared to be suffering from their 3-2 defeat at Port Vale last Saturday.
As a result, Walsall were generally the more dangerous but they could not breach the Barnsley rearguard until the second half.
Leary, a recent signing from Luton, put his mark on the game early in the tie when he went close to opening Walsall's account with a long-range dipping shot which whistled just over the bar.
Mark Wright and James also went close but Walsall's best opportunity occurred when James beat goalkeeper Nick Colgan only to see Carbon race back to clear the ball off the line.
But the longer the game progressed, the more obvious it became that there was little to choose between either side despite Barnsley's lack of firepower from Paul Hayes and Tommy Wright.
Walsall, without a goal in four of the last five league home games, struggled to make any impact at the start of the second period after sending on Michael Standing and Chris Westwood for Simon Osborn and Ian Roper.
Carbon, meanwhile, continued to be the mainstay of the Barnsley defence as he repeatedly foiled Walsall's lightweight attack when the Yorkshire club went through an anxious spell.
Only a brave save by Colgan prevented Ishmel Demontagnac from opening the account.
Walsall's smallest crowd of the season became increasingly frustrated by the inability of their side to gain the upper hand.
In the 68th minute, however, Walsall were finally rewarded for their persistent pressure when Leary opened the scoring.
Leary took a delightful through ball from Mads Timm and glided around Colgan before slipping the ball into the net with a cross-shot.
Barnsley continued to struggle in attack and Walsall gained in confidence after taking the lead and capped a good performance to seal the match with a second goal from James when he headed home from close range.