In partnership with his brother James from 1797 to 1807, in which year James moved to London where he was a military instrument maker, music seller and publisher.

William Power continued the business, initially (until 1810) under the name Power & Co. (a name which had been in use since 1803) at 4 Westmoreland Street and then under his own name until 1831.

William Power invited Thomas Moore to cooperate in a projected edition of Irish airs. The first volume Selection of Irish melodies, with symphonies and accompaniments by Sir John Stevenson, Mus. Doc., and characteristic words by Thomas Moore Esq. was published c. 1807/1808. There followed nine additional issues and a supplement, containing a total of 124 airs. As a result of disagreement between William and James, the later numbers were issued by the latter’s firm in London with arrangements by Henry Bishop (Boydell, 'Music, 1700–1850'). An insert into the third edition of Thomas Moore's Lalla Rookh in 1817 stated: 'The Publishers [Longman, Hurst, Rees, Orme, and Brown (Paternoster-Row, London)] beg to inform the Composers of Music and Music Sellers, that Mr. James Power, of the Strand, Music Seller, is the only person authorised by them to publish the Songs or Verses in this Work connected with Music'.

William Power was a subscriber to the Melodia Sacra in 1814.

Succeeded in business by Marcus Moses in 1831.

[Dates and addresses differ according to sources: Teahan gives the date of 1810 only. Humphries & Smith and Hogan give the dates as c. 1802 to 1831 at 4 Westmoreland Street. Waterhouse gives the dates as 1807 to 1831 at 4 Westmoreland Street.]