The Czech-born American took charge of an hour-long coaching session at Queen's Club in London.
Murray will play France's Nicolas Mahut in his Aegon Championships opener, but rain delays mean the match is unlikely to start before 14:00 BST.
Murray and Lendl's morning practice was cut short by the weather and more rain is forecast through the day.
Lendl arrived from the United States on Monday evening, having last week agreed a deal to resume his coaching role alongside Murray.
The pair split in March 2014 after a successful two-year period that saw Murray win his only Grand Slam titles at the US Open and Wimbledon, as well as Olympic gold.
Their practice session on Monday lasted an hour before the rain arrived, with British number seven Alex Ward providing the opposition across the net.
Lendl worked in tandem with Jamie Delgado, who joined Murray's coaching set-up earlier this year, with the former world number one directing the drills.
Mahut, ranked 51st, should provide a stern test of Murray's grass-court level when the pair meet, the Frenchman having won an ATP title on the surface in the Netherlands on Monday.
Murray, a four-time champion at Queen's Club, lost to Mahut in the second round in 2012.

Alicia Moran, 14, was last seen at her home in the Linthwaite area of Huddersfield at 16:30 BST on Sunday.
She was found earlier in Bristol after previous sightings of her in Manchester, West Yorkshire Police said.
A police spokesperson said a 24-year-old man from the Bristol area had been arrested in connection with her disappearance.

Emergency services, including an air ambulance were called to Coate Water, Swindon at about 19:30 BST on Friday, after reports a girl had collapsed.
Wiltshire Police said the 17-year-old was pronounced dead at the scene. Officers do not believe the death to be suspicious.
A spokesman said: "Our thoughts remain with the girl's family and friends at this extremely difficult time."
Ivan Lendl returned to coaching duties with Andy Murray for the first time in over two years on Tuesday.
[NEXT_CONCEPT]
A missing girl has been found safe and well while a man who was with her has been arrested, police have said.
[NEXT_CONCEPT]
A teenage girl has died after suffering a cardiac arrest in a Wiltshire park.