[6] From the age of 9, Walenn was a choir boy and sang solos in some of the principal churches and cathedrals in Britain.
[5][8] Beginning in April 1887 Walenn performed with the D'Oyly Carte Opera Company, first in its European tour that ended in February 1888, as a chorister and understudy.
[2] Finally, in September 1891, Walenn was promoted to play principal comic roles regularly in one of D'Oyly Carte's touring companies.
[11] His roles over the next dozen years were Jack Point in The Yeomen of the Guard, the Duke of Plaza-Toro in The Gondoliers, Bumbo in The Nautch Girl, Bedford Rowe in The Vicar of Bray, the McCrankie in Haddon Hall, Bunthorne in Patience, Scaphio in Utopia, Limited, Dick Deadeye and later Sir Joseph Porter in H.M.S.
Pinafore, Peter Grigg in The Chieftain, Pish-Tush and later Ko-Ko and the title role in The Mikado, Mr. Cox in Cox and Box, Grand Duke Rudolph in The Grand Duke, the Lord Chancellor and later Lord Mountararat in Iolanthe, King Ferdinand and later Boodel in His Majesty, and John Wellington Wells in The Sorcerer, Prince Paul in The Grand Duchess of Gerolstein, King Ouf in The Lucky Star, the Usher in Trial by Jury, Hassan in The Rose of Persia, Pat Murphy and later Professor Bunn in The Emerald Isle and Mons.
[2] From December 1905 to October 1907 and from October 1908 to March 1909, he joined another D'Oyly Carte touring company, playing the Learned Judge in Trial, Sir Joseph in Pinafore, General Stanley in Pirates, Bunthorne in Patience, the Lord Chancellor in Iolanthe, Gama in Princess Ida, Ko-Ko in Mikado, Jack Point in Yeomen, and the Duke in Gondoliers.
His last role on the London stage was Cyrus Wykoff in the comedy Daddy Long Legs at the Victoria Palace (1933–1934).