Match ends, Dartford 2, Tamworth 3.
Kevin Thornton's second-half brace saw Tamworth claim three points at Dartford and seal the home side's relegation.
Elliot Bradbrook put the hosts ahead early on but the visitors levelled thanks to Jessy Reindorf.
Kenny Clark felled Kaiyne Woolery after the break and Thornton fired home the resulting penalty.
Thornton grabbed a third in the final minute and despite Bradbrook's late consolation, Dartford were down.
Dartford manager Tony Burman told BBC Radio Kent:
"It's a disappointing day for us and a disappointing season all round in all fairness. We've had a go but we just couldn't cross that line.
"The club has been riding along nicely and it's been doing well and I'm sure there will be better times for us in the future.
"I'm devastated that I've put the club in this position - relegation is not a nice thing to happen.
"When you're winning you're the best manager in non-league football and when you're not, you're the worst."
- 14Mitchell-KingSubstituted forClarkat 26'minutes
- 31StevensonSubstituted forSuarezat 68'minutes
- 4SterlingSubstituted forWoodyardat 90+4'minutes
- 10BradbrookBooked at 90mins
- 7KerrySubstituted forBakerat 90+4'minutes
- 6Richards-EvertonBooked at 43mins
- 12CapriceBooked at 81mins
- Craig Hicks
- Shots on Target
Second Half ends, Dartford 2, Tamworth 3.
Substitution, Tamworth. Richard Baker replaces Lloyd Kerry.
Substitution, Dartford. Alex Woodyard replaces Tyrone Sterling.
Goal! Dartford 2, Tamworth 3. Elliot Bradbrook (Dartford) right footed shot from the centre of the box to the bottom right corner.
Elliot Bradbrook (Dartford) is shown the yellow card for dissent.
Goal! Dartford 1, Tamworth 3. Kevin Thornton (Tamworth) left footed shot from the centre of the box to the bottom left corner.
Foul by Jack Evans (Tamworth).
Ben Swallow (Dartford) wins a free kick.
Attempt missed. Kevin Thornton (Tamworth) right footed shot from the centre of the box misses to the left.
Attempt missed. Kevin Thornton (Tamworth) right footed shot from outside the box misses to the left.
Foul by Ben Swallow (Dartford).
Richard Peniket (Tamworth) wins a free kick.
Attempt saved. Lloyd Kerry (Tamworth) right footed shot from the centre of the box is saved.
Attempt missed. Kaiyne Woolery (Tamworth) right footed shot from outside the box is too high.
Jake Caprice (Tamworth) is shown the yellow card.
Foul by Jake Caprice (Tamworth).
Danny Harris (Dartford) wins a free kick.