Wasim has led Lancashire to the NatWest Trophy and AXA League titles in the last two days, and the county are still in contention to take their first outright Championship since 1934 in the next two weeks.
But the Lancashire committee still decided yesterday to sign a new overseas player.
Murali, whose unusual action was at the centre of the recent controversy surrounding former Lancashire coach David Lloyd, will joint he county when Sri Lanka complete their World Cup commitments in June, and Lancashire expect him to play in around half of their Championship matches and two thirds of their one-day fixtures although they are still waiting for the dates of Sri Lanka's home series against Australia to be confirmed.
Chairman Jack Simmons said: ``This is a major signing for Lancashire of one of the outstanding talents in world cricket. It is an indication of the ambition of the club to get trophies in the cabinet.
``This man is a devastating spinner and I am looking forward immensely to watching him at Lancashire. I am sure he will attract new spectators to the ground.''
Coach Dav Whatmore, who worked with Murali in the last World Cup, added: ``I know Muri well and I confident he will be a great asset to the team. There is no doubt he is a true matchwinner. ``Both Mike Atherton and John Crawley were highly impressed by him during the Oval Test.''
Groundsman Peter Marron seems certain to be asked to produce some turning pitches at Old Trafford next season, which could also be good news for young leg-spinner Chris Schofield - although spare a thought for Gary Yates, who has just seen off the challenge of Mike Watkinson only to see Lancashire sign one of the best two off-spinners in the world.
Simmons was also keen to place on record the county's appreciation of Wasim's efforts since joining them in 1988. ``He has been a wonderful servant to lancashire and one of the great ambassadors of cricket,'' he said.
``Murali's contract is for one season and Wasim will be under consideration as the overseas player for the year 2000.''
Lancashire have yet to announce who will succeed Wasim as captain, although it seems certain to be Crawley, who has impressed everybody at the club in his first year as vice-captain.