The club’s new vice-captain followed his all-round heroics against Barbados on Saturday with a hard-hitting 77 off just 39 balls at the expense of Hampshire’s bowlers in the semi-final.
Rob Newton supported well with 52 from 37 deliveries as the Steelbacks reached 170-5 in their 20 overs.
Hampshire were then dismissed for 138 - giving Northamptonshire victory by 32 runs - and although Willey, Josh Cobb and Rob Keogh picked up two wickets apiece it was teenager Saif Zaib who produced the most eye-catching bowling figures.
He claimed 3-24 in his four overs of left-arm spin - numbering England Lions batsman James Vince among his victims.
The final against Nottinghamshire went less well for the County who could only manage 122-9 despite the best efforts of Cobb (22), Olly Stone (20), Steven Crook (17) and skipper Alex Wakely (16).
Nottinghamshire reached their target at 126-3 with three overs to spare, thanks largely to former Northamptonshire man Riki Wessels with an unbeaten 59.
The squad now turns its attentions to red-ball cricket and a two-day match against Warwickshire starting on Tuesday.