 Kọ itẹsiwaju fun paragirafi yii - Forrest ni a bi ni Ilu Lọndọnu, ọmọ keji ti Lieutet-Colonel William Forrest ti Ogun Bengal, ati iyawo rẹ, Georgiana Christina Carmichael-Smyth, ọmọbinrin James Carmichael Smyth ati arabinrin Sir James Carmichael-Smyth, 1st Baronet. O darapọ mọ ọmọ ogun gẹgẹbi cornet ni ọdun 1836, ati pe o ni igbega si alaga ni ọdun 1839, olori ni ọdun 1841, pataki ni 48, brevet lieutet-colonel ni ọdun 1854, lieutet-colonel ni ọdun 1859, ọgagun ni ọdun 1860, olori-ọga ni ọdun 1868, lieutet-general ni ọdun 1877 ati gbogbogbo ni kikun ni Oṣu Keje 1, ọdun 1881. O ja ninu Ogun Crimea o si kopa ninu Ikọlu ti Brigade ti o wuwo ni Balaclava : ó ṣe tán. Wọn yàn án gẹgẹ bíi CB ní ọdún 1875 ní ayẹyẹ ọjọ ìbí. 