When the uprising against the Dahije in Šumadija broke out in the beginning of 1804, Lazarević joined the rebels.
The uprising spread over Kolubara, with Jakov Nenadović from Valjevo reaching Šabac.
In a short time, Lazarević became one of the leading fighters in the band, and eventually the leader of the Tamnavci and Posavci of Šabac (the rebels from the Tamnava and Posavina areas in the Šabac nahiya).
When the ordinary leader of the Šabac rebels was to be appointed, at a time when Mateja Nenadović pursued that rank (his uncle Jakov commanded the northwestern Valjevo nahiya), the supreme rebel leader Karađorđe asked the Tamnavci and Posavci on whom to pick.
In unison, they chose Lazarević.
Petar Moler cut his beard, and he then went with Jakov and others towards Užice.
He then married Danojla from Jadar, with bishop Antim of Valjevo marrying them as his kum.

From 1805, when the rebels fought for liberation, against the Ottoman Empire, Lazarević had several important victories in which he fought heroically and with vojvoda tact and authority.
On  18 January [O.S. 6 January] 1806 Jakov Nenadović and Luka Lazarević began the siege of Šabac, while Karađorđe set off from Belgrade to join them; on the way Karađorđe learnt that Ottoman Bosnian troops were about to cross the Drina and thus immediately dispatched Lazarević.
Arriving at Lešnica on 29 January [O.S. 17 January] 1806 with Živko Dabić, Lazarević's unit defeated the Turks at Ranitovac after a day of fighting, with much of enemy troops drowning in the Jadar river.


 
He was nearly killed at the Battle of Mišar (August 1806), but was instrumental in the victory; Karađorđe ordered Lazarević to hide in the woods with cavalry, and on the sound of his cannon, charge into the rear of the Ottoman troops.
In the midst of battle, Lazarević had a duel with Ottoman Bosnian commander Mehmed-beg Kulenović, and was severely wounded, as riflemen shot at the two.
Lazarević managed to escape into the woods, while Kulenović fell.
The destroyed Ottoman army retreated towards Šabac, while Lazarević was sent to Provačka Ada for treatment.

When the Ottomans handed over Šabac to the Serbian rebels on 2 February [O.S. 25 January] 1807, Karađorđe left Lazarević as commander with 1,000 soldiers.
As the supervisor of Šabac, he worked on implementing order in the town and district, and sometimes judged at the magistrate and entered judgements into the protocol.

Lazarević led battles between Šabac and Loznica, and at Užice avenged his cousin Ranko.
He also fought on the other side of the Drina, at Glavice above Bijeljina (where Meho Orugdžić fell), between Zvornik and Srebrenica, and destroyed Ottoman troops crossing towards Sarajevo.
The winning streak was stopped by the defeat at Čegar (May 1809).

The epic poet and guslar Filip Višnjić (1767–1834) enumerated Lazarević's most famed battles as Loznica (October 1810), where he wrested the control of the town from the Ottomans, and Novo Selo on Krstovdan, where he killed Pejzo Mehmed-Aga.
The epic poem of the latter glorifies his bravery, and also describes him as a very good strategist.
When the uprising against the Dahije in Šumadija broke out in the beginning of 1804, Lazarević joined the rebels. The uprising spread over Kolubara, with Jakov Nenadović from Valjevo reaching Šabac. In a short time, Lazarević became one of the leading fighters in the band, and eventually the leader of the Tamnavci and Posavci of Šabac (the rebels from the Tamnava and Posavina areas in the Šabac nahiya). When the ordinary leader of the Šabac rebels was to be appointed, at a time when Mateja Nenadović pursued that rank (his uncle Jakov commanded the northwestern Valjevo nahiya), the supreme rebel leader Karađorđe asked the Tamnavci and Posavci on whom to pick. In unison, they chose Lazarević. Petar Moler cut his beard, and he then went with Jakov and others towards Užice. He then married Danojla from Jadar, with bishop Antim of Valjevo marrying them as his kum.
From 1805, when the rebels fought for liberation, against the Ottoman Empire, Lazarević had several important victories in which he fought heroically and with vojvoda tact and authority. On  18 January [O.S. 6 January] 1806 Jakov Nenadović and Luka Lazarević began the siege of Šabac, while Karađorđe set off from Belgrade to join them; on the way Karađorđe learnt that Ottoman Bosnian troops were about to cross the Drina and thus immediately dispatched Lazarević. Arriving at Lešnica on 29 January [O.S. 17 January] 1806 with Živko Dabić, Lazarević's unit defeated the Turks at Ranitovac after a day of fighting, with much of enemy troops drowning in the Jadar river.

 
He was nearly killed at the Battle of Mišar (August 1806), but was instrumental in the victory; Karađorđe ordered Lazarević to hide in the woods with cavalry, and on the sound of his cannon, charge into the rear of the Ottoman troops. In the midst of battle, Lazarević had a duel with Ottoman Bosnian commander Mehmed-beg Kulenović, and was severely wounded, as riflemen shot at the two. Lazarević managed to escape into the woods, while Kulenović fell. The destroyed Ottoman army retreated towards Šabac, while Lazarević was sent to Provačka Ada for treatment.
When the Ottomans handed over Šabac to the Serbian rebels on 2 February [O.S. 25 January] 1807, Karađorđe left Lazarević as commander with 1,000 soldiers. As the supervisor of Šabac, he worked on implementing order in the town and district, and sometimes judged at the magistrate and entered judgements into the protocol.
Lazarević led battles between Šabac and Loznica, and at Užice avenged his cousin Ranko. He also fought on the other side of the Drina, at Glavice above Bijeljina (where Meho Orugdžić fell), between Zvornik and Srebrenica, and destroyed Ottoman troops crossing towards Sarajevo. The winning streak was stopped by the defeat at Čegar (May 1809).
The epic poet and guslar Filip Višnjić (1767–1834) enumerated Lazarević's most famed battles as Loznica (October 1810), where he wrested the control of the town from the Ottomans, and Novo Selo on Krstovdan, where he killed Pejzo Mehmed-Aga. The epic poem of the latter glorifies his bravery, and also describes him as a very good strategist.
Luka Lazarević