In a lively opening, both clubs had chances to open the scoring but from the quarter-hour mark onwards, Vale controlled the contest and deservedly cruised to victory courtesy of goals from Kian Harratt, James Wilson and Malvind Benning.
Vale's efforts were made easier when Mansfield's Oliver Hawkins was sent off for two yellow cards in the 35th minute and the Stags will remain at the fourth tier of English football.
The Staffordshire outfit opened the scoring through Huddersfield Town loanee Harratt, who had not found the back of the net since a double against the same opponents on March 15.
The 19-year-old timed his run perfectly to send a header into the bottom corner, and star man Wilson soon doubled the advantage with a header of his own on the rebound after a previous header had hit the crossbar.
Things got worse for Mansfield with 10 minutes of the first half remaining as Hawkins was dismissed for two cautions in the space of five minutes, leaving the Nottinghamshire side with an uphill task after the break.
To their credit, they kept the margin at two goals but Vale wrapped up the contest with five minutes remaining as former Mansfield man Benning sent a volley at the back post into the far bottom corner, capping the perfect day for Darrell Clarke and his side as they return to the third tier after a five-year absence.