United suffered a 1-0 defeat to Chelsea Women in the final of this competition last term but exacted revenge after Lucia Garcia scored twice in a comfortable win on Sunday.
Ella Toone's eye-catching strike in the first half set the tone before a goal for Rachel Williams and Garcia's double added gloss to a convincing scoreline, despite Beth England hitting the crossbar for Spurs.
Marc Skinner's side dominated the opening half as Millie Turner saw a header cleared off the line by Martha Thomas, while Williams headed over.
However, there was no stopping Toone on the stroke of half-time as she exchanged passes with Lisa Naalsund before arrowing a rocketed right-footed finish into the top corner from the edge of the area.
Further punishment followed for an underwhelming Tottenham after the interval when Williams headed down from Katie Zelem's free-kick to double United's lead in the 54th minute.
Goalkeeper Becky Spencer then handed Skinner's team more joy just three minutes later, mindlessly playing straight to Garcia, who slotted into an empty net.
Garcia capped the scoring after 74 minutes, receiving an offload from Turner before curling a delightful finish past the powerless Spencer as United secured their first major trophy in club history.
Data Debrief: United ease pain of last year
United fell short last year against Chelsea but continued their impressive record against Spurs here, extending to 13 games unbeaten against Tottenham since being founded in 2018.
This defeat will remain painful for Spurs in their first FA Cup final appearance, also ending a seven-game undefeated streak since losing to rivals Arsenal at the start of March.
The Red Devils swept aside Tottenham Women with a 4-0 victory at Wembley Stadium as Ella Toone and Rachel Williams were on target before Lucia Garcia's second-half double.
United missed out in the final of the Women's FA Cup last season, losing to Chelsea 1-0, but produced an emphatic response to secure the first major trophy in their history.
Having lost in Champions League qualifying, suffered group-stage elimination in the League Cup and sitting fifth in the Women's Super League, Skinner was delighted with his side's response in the capital.
The United boss told BBC One: "We are obviously not where we want in the league, right? But we are history-makers for Manchester United.
"I didn't need to remind the owners of that, they know. There is a lot of support and love for our team and the growth.
"We want to compete for titles but you all know how important adding that first piece of silverware is. We've got nothing but growth ahead."
Toone provided the first moment of magic with a rocketed right-footed finish into the top corner from the edge of the area, setting the tone on the stroke of half-time after a dominant opening 45 minutes.
"In all honesty, I felt that first half was just frustration because we didn't score, I thought we offered more of a threat, we controlled most of their threat," Skinner added.
"As much as I am exhausted now, it is a magical feeling. Tooney scored one of those goals at Leicester but it is another thing to do it at Wembley.
"I told her on the podium you have to feel it, remember it because it comes and goes too quick, and that is what she did. Congratulations to her and the team, we are FA Cup winners."
Williams added the second with her headed finish after 54 minutes, though the United forward admitted this season has been far below usual standards.
"We don't like to admit it but it does mask over the issues we've had," Williams told BBC One.
"We have had some ups and downs this year. That's for Marc [Skinner] and the backroom staff to be like 'right this is what we have to do in the summer'.
"We are going to have change things next year. We have had some injuries, three or four ACLs, at the start of the season. That's football, teams go through transition.
"You have a good year, you have a dip. Next year we might just come back bigger, better and stronger and who knows we might just be lifting the league."
