The 34-year-old, who became just the second man to complete the long-distance double-double at Rio 2016, will switch his attention to the roads after next week's meet in Zurich and signed off in his last race on home soil by winning in seven minutes and 38.64 seconds.
Farah, who won 10,000m gold and 5000m silver at the IAAF World Championships in London this month, sat in the middle of the field before making his trademark push with 600m remaining, taking the lead for his own on the final lap.
He paid tribute to the fans in Birmingham and expressed his excitement about moving on to the next stage of his career.
"Emotions were high, not as high as London, but it was the last time at home and I really enjoyed it," Farah told BBC Sport. "This is what it's all about.
— IAAF Diamond League (@Diamond_League) August 20, 2017
"All I dreamed of as a youngster was racing for Great Britain. I want to continue to see what I can do on the road without having a target on your back and the pressure.
"It can get a little hard when you have some pressure. Going to the road it's going to be a new game and I'm excited."
Elaine Thompson put her disappointment of missing out on a 100m medal at the Worlds by beating Josee-Marie Ta Lou with a time of 10.93secs – Dafne Schippers coming sixth.
Ekaterini Stefanidi took gold at the Worlds and she extended her winning streak to 12 competitions by clearing 4.87m in the pole vault, while Ramil Guliyev followed up his 200m triumph in London with another victory to earn a place at Zurich.
Nijel Amos bounced back from missing out on a medal in London by taking his fourth Diamond League win of the season in the 800m and Allyson Felix was beaten by 19-year-old Salwa Eid Naser in the 400m.
Mutaz Essa Barshim almost bowed out of the high jump at 2.31m and 2.39m but went on to record a world-leading leap of 2.40m for a comfortable win.
Photo Getty Images. Caption: Mo Farah celebrates winning the 3000m in Birmingham