City won 2-1 at Reading to make it 24 games unbeaten and secure promotion to the Sky Bet Championship for the first time in 65 years.
Ryan Oné had given the Imps an early lead, but the Royals struck back with a stoppage time free-kick from Lewis Wing.
However, there was a final string in the tale for the hosts as Jack Moylan struck a winner just moments later to send the Imps fans into raptures.
Michael Skubala made three changes to the side that defeated AFC Wimbledon on Good Friday. Friday's matchwinner Oné was rewarded with a start against the Royals, coming into the side for Rob Street. There were also places in the starting line-up for Ivan Varfolomeev and Dom Jefferies, who replaced Tom Bayliss and Moylan.
The Imps got off to a brilliant start, striking first through Oné in the fifth minute. Varfolomeev was fouled by Charlie Savage on the right flank and City were awarded a free kick. Reeco Hackett delivered into a crowded penalty box where Oné rose highest to meet it, directing his header past the outstretched arm of Joel Pereira.
Just three minutes later, City thought they have a second but the joy was short-lived. Jefferies engineered a lighting fast counter attack for the Imps and laid the ball off for Hackett. He delivered low towards Oné who tapped the ball in, but he had just strayed offside.
Soon after, the home side looked to respond. Lewis Wing tried a couple of efforts, with the last deflecting off Ben House for a corner. The delivery was dealt with by City though.
With 19 minutes played, Tom Hamer speared in a long-throw which was cleared as far as Conor McGrandles. He lifted it back in for House at the far post who headed the ball back across the six-yard box, forcing Jeriel Dorsett to turn the ball behind. The resulting corner was delivered by Hackett, but the home side cleared their lines.
Two minutes after, Daniel Kyerewaa went down in the area under pressure from Tendayi Darikwa, but the appeals from the home side were waved away.
The pressure from the Imps had been relentless in the opening exchanges. The Royals defenders had to stay switched on, with City continuously putting them under pressure with balls in the box.
After half an hour, Savage rode a challenge from McGrandles but with options either side, he elected to shoot, dragging his effort wide from 25 yards.
The Imps then had to withstand some pressure from the hosts but won the ball back and broke quickly. Oné exchanged passes with Hackett before going through on goal, but the hosts managed to get numbers back to crowd him out before he could take aim.
On 40 minutes, there were two chances for City. Jefferies saw an attempt turned away by Perreira before Ryley Towler lifted an effort just over the bar.
Early in the second period, Wing looked to thread the ball through for the run of Savage, but it was cutout by an excellent sliding challenge from Jefferies.
Following three City changes around the hour mark, the Imps came close to adding a second, with substitute Alfie Lloyd turning a Towler cross off target with a header.
The Imps came close again in the 73rd minute, as they counter-attacked through substitute Street, who laid the ball off for Darikwa on the left flank. He centred the ball low towards Lloyd, but Paudie O'Connor, slid in to thwart him from close range.
Soon after, the Royals looked to press City with crosses into the area of their own, but a couple of good defensive headers from Sonny Bradley denied them a heading opportunity in the box.
There were eight minutes of time added on and in the first minute of those, the hosts levelled through a sweetly struck free-kick from 20 yards by Wing.
Nevertheless, as has been a common theme this season, the Imps weren't done and scored just four minutes later through Moylan, who was played in by McGrandles and took his time before firing home the clincher from the right side of the penalty area.
City held on and clinched a famous victory to seal promotion to the second tier.
Imps: Wickens, Darikwa, Towler, Hackett (Moylan, 83), McGrandles, Bradley, Jefferies (Elerewe, 67), House (Street, 60), Oné (Lloyd, 67), Hamer, Varfolomeev (Bayliss, 83).
Subs: Jeacock, Ring.
Reading: Pereira, Dorsett (Young, 82), O’Connor, Burns, Kyerewaa, Fraser (Keane, 70), Wing, Nyambe (Roberts, 70), Savage, Doyle (Lane, 28), Ehibhatiomhan.
Subs: Yiadom, Rinomhota, Stevens.
Attendance: 17,144 (2,844 away).
