United started well but Miedema poked in the opener from Dominique Bloodworth's precise through ball.

The Dutch forward made it two when she lashed past Siobhan Chamberlain before Beth Mead headed against the bar.

Molly Green's low finish pulled one back for United late on but they could not create any further opportunities.

Arsenal will play Manchester City at Sheffield's Bramall Lane on 23 February in a repeat of last season's final, which the Gunners won 1-0.

Netherlands striker Miedema showed a clinical streak with both of her finishes, making it 12 goals in her past 11 games in the competition.

Joe Montemurro's Arsenal - second in the Women's Super League - have now reached seven of the eight League Cup finals, going on to lift the trophy on five occasions.

United, managed by former England centre-back Casey Stoney, were competitive throughout but struggled to create clear openings.

Arsenal striker Vivianne Miedema:

"I am happy that I could help the team again and we are in the final again, and we just need to get ready for that.

"We didn't play that well but I thought we controlled the game after we scored the first goal.

"We made it harder than it had to be but we are just happy with the win."

Manchester United head coach Casey Stoney:

"I am really proud of my team - at 2-0, they could have collapsed but they didn't. They got stronger. They fought.

"It was not our greatest performance in possession and I thought we got out of our shape a couple of times, which cost us.

"But you know, we are seven months in. We have got a very young team and we have just gone and lost 2-1 to Arsenal in a cup semi-final, and actually got stronger as the game went on, so I am super, super proud of the team."