Although Livingstone’s wicket just as he was beginning to motor turned the game in Somerset’s favour, some outstanding fielding contributed to their victory.
Kohler-Cadmore claimed two catches inches above the turf, and Gregory and Migael Pretorius also took stunning diving efforts.
Earlier, new dad Kohler-Cadmore was the only Somerset batter to find any real timing on a sticky pitch, striking six fours and four sixes as he looked on course to make the first century at Finals Day.
Lancashire paceman George Balderson (3-31) had him caught on the boundary but Craig Overton and Pretorius helped Somerset to an above par score by hitting Tom Aspinwall for 21 off the final over.
Alongside the controversy of Livingstone’s dismissal, Lancashire also made an unusual move at the start of the 19th over, retiring Balderson who had seven off six balls, and replacing him with Tom Hartley.
It backfired as Hartley chipped Ben Green to Kohler-Cadmore first ball.
James Anderson took 2-34 in what might be his last Finals Day and came out to bat as the rain arrived in Birmingham with Somerset strolling to victory by 23 runs.
The 2023 champions have the chance to avenge last year’s defeat by West Country rivals Gloucestershire in the final which is due to start at 18:45 BST.