Gilder finished the event at 8-under, three shots clear of Raymond Floyd, Bobby Walzel, Gil Morgan and defending champion Bruce Fleisher. Walzel, Morgan and Fleisher each carded Sunday 70s, while Floyd came home in 67.
Floyd led the tournament through 13 holes of his final round, but bogeyed the par-5 14th and par-4 15th holes to finish three off the pace.
Overnight leader Hale Irwin fell into a tie for ninth place at 3-under following a 3-over-par 74 on Sunday. First-round leader Jack Nicklaus ended the event in a tie for 20th at even par after shooting a 4-over-par 75.
'Of course it's disappointing,' said Nicklaus, whose last victory came in the 1996 Tradition. 'I felt good this morning, I felt composed and felt very confident about what I was going to do.'
Gilder's start on the Senior Tour is similar to the way he began his PGA Tour career 25 years ago. Gilder won the first of six PGA Tour titles in just the second tournament of his 1976 rookie season. This week's victory comes in his third Senior appearance. It's his first title since the 1983 Phoenix Open.
'That was a long time ago,' said Gilder, who earned $210,000. 'When you haven't won for that long, you wonder a little bit if it will happen again.'
Gilder becomes just the second Senior Q-School medallist to win in his first season. Allen Doyle won four times in 1999, the year after winning the Qualifying Tournament.
Click here for Full-Field scores from the Verizon Classic!