The news of Welsh's re-signing comes after a week of speculation that suggested the 26-year-old was disgruntled with the offer put forward by the Bombers, and was considering a move to another club.
Welsh, along with St Kilda midfielder Luke Ball, had been heavily linked with Collingwood, but the deal extension will now see the 145-game player notch up at least 10 years of service in the red and black.
Meanwhile, Lovett-Murray has overcome a tumultuous season to earn another two years at Windy Hill.
The tall backman was charged with possession of drugs and driving while unlicensed in August.
The club vowed to stand by him and did not offer any additional punishment. He will appear in court later this month.
Essendon general manager of football operations Paul Hamilton said the pair of re-signings was a coup for the club.
"Andrew and Nathan are two of the real leaders at the club and as two senior players with strong bodies they will be important to our future success," he said on Monday.
"Nathan played some really good football this year and, while Andrew was restricted with a serious leg injury, he returned and also showed what he is capable of.
"They will both now have a big pre-season and we expect them to be primed for 2010 and show their trademark courage and determination on the field."
Lovett-Murray is due to play his 100th match in round one next year.
Meanwhile, negotiations with out-of-contract McPhee have continued with the Bombers yet to re-sign the 27-year-old.
The club remains committed to reaching an agreement to retain the 167-game player, despite reports he is considering a return to former club Fremantle through the NAB AFL Pre-season Draft.
