HOT-SHOT Matty Clements was at the double for the second round in a row as the Linnets reached the Dr Martens League Cup final for the first time.
Lynn made it third time lucky after being put out in the semi in the last two years.
Glen Fuff and Simon Dakin of Tuesday's squad are the only ones to have played in all three semi-finals.
Clements has scored all of Lynn's five goals in the past three games and is joint leading scorer (seven) with another on-loan forward, Norwich's Danny Bloomfield.
"It's a great result for the club," said acting manager Kevin Boon. "Matty was the star of the show, but it's what the fans and the people upstairs deserve.
"It's also part of Tony Spearing's team, while the fans' support this year has been tremendous.
"We gave the team a kick up the rear at half-time, asking if they were committed to King's Lynn FC."
After Lee Hudson's early turn-and-shot went wide, the best chance of a gritty first half fell midway through to Kevin White. He missed a sitter of a header from six yards.
Boro had plenty of pressure but little to show for it.
Just before the hour mark Clements opened the scoring with a 'peach'. He outpaced two defenders down the middle and deftly lifted the ball which bounced and bobbled before finding the net over the advancing keeper.
Wayne Anderson, again like Saturday coming on for Tommy Wright at half-time, had an effort cleared off the line, while Dakin went close with a snap-shot.
But ten minutes from time Simon Hollis headed home a disputed free-kick given by the referee, who was unpopular or booking Glen Fuff for elbowing, but not yellow-carding Borough for the same offence.
This did not deter Lynn, who grabbed the winner with five minutes to go with the best move of the tie.
Sub Dave Robinson won the ball in defence, switched it to Adie Hayes, who played a one-two with another sub Paul Watts before directing a perfect through-ball to Clements, who slotted past keeper Brendan Murphy.
It is The Walks outfit's first final since the Norfolk Senior Cup in 1994, while their only previous League Cup win was in 1982/83 when they were in the Northern Premier.
Lynn: Wilson, Dakin, March, McNeil (Robinson 68), Fuff, Rowe, White, Hayes, Clements, Hudson (Watts 76), Wright (Anderson 45).
Solihull: Murphy, Hamilton, Hier (Campbell 43), Smith (Anshad 90), Knight, Cooper, Hollis, Smith (Pippard 73), Hall, Amos, Dutton.